I find this thread very interesting so I am going to contribute to it. (For what it's worth
)
I think a lot of it comes down to attitude and circumstances and as I was to discover boundaries.
I have been with my husband now for 21 years when we first started dating he was in a relationship (that he was trying to end) but he didn't tell me that at the time.
We started seeing each other and I found out about her when she came to his workplace found some of my clothes in a work bag of his and ripped them to pieces and basically had to be physically restrained otherwise she would have attacked me.
He explained that he had tried to end it with her many times but she kept on coming back.
She lived in France and he lived in England and she kept on catching the euro star and coming back into London
He explained that when she stayed in England they no longer slept together and actually I believed him because when we first got together he had erectile dysfunction (and also with her in the end of their relationship) because he felt a bit hurt himself as if he was being forced to be in a relationship he didn't want to be in. Also she had been trying to get pregnant even though he didn't want a baby!
Again I found evidence of this later on when I found a pregnancy test under the bed that thank god was labelled negative!
So it might be an unpopular opinion but sometimes when a man gives you the line I am stuck in a unhappy relationship and I want to leave sometimes he is telling the truth! (Although as I saw later it's more complicated than that!) Why do any of us get trapped unless we are not aware of what it is we really need?
However it does happen sometimes that people get involved with someone who turns out to be a narcissist and they end up in a kind of hostage situation! (This applies to both men and women and actually in this situation it was just a case of top trumps because in many ways she found his disinterest a challenge even interesting but who then who stays in a relationship with a person who in some horrible way gets a kick out of being rejected unless they themselves like to be with someone with very low self esteem?)
Fast forward 21 years later and we have both been through a lot! He wanted rescuing well I did that but then you find out that a man who expects to be rescued doesn't have very good boundaries in place and actually needs to take responsibility for his own life and not expect others to do it for him!
So we all reap what we sow....
I think that's unavoidable and if you come from a troubled background like myself and my husband and his former girlfriend then expect to have troubled relationship's with others?
I don't think that anyone willingly sets out to hurt others unless they are a sadist or sociopath (as others have mentioned) but I think especially when you are young you can be blissfully ignorant of the trouble or pain you can cause.(also pain or conflict can be your normal)?
His former girlfriend was willful and possessive my husband was weak and I was naive and addicted to being a carer and caretaker all 3 of us have suffered because of that
At the end of the day you have to live with yourself and the consequences of your actions if you mature and wise up and develop empathy that's going to hurt if previously you were all about self gratification or what is worse repeating negative patterns of relating (,or not as the case may be) which you have picked up from your parents or family?
So there are many different ways of looking at things but the main thing in all of this to me is having boundaries.
Something I have had to force myself to do because I didn't know any better.
That's been painful and as regards to cheating I found that actually my husband did cheat but it wasn't in the sexual sense but he cheated me by not being the person he claimed to be and by being both childish and vindictive at times. (Typical narc behaviour include gaslighting as well but I didn't know it at the time!).
So I felt robbed of a husband and a future we should have had because he gave me a lot but he didn't (couldn't) love me.
Although he tries but it's not really in him it's like he has an emotional deficit and no amount of love from others can fill it?
So I was the other woman at first (unwittingly) and I think it's interesting to note the structure of this i.e the love triangle!
That is a favourite of narcissists everywhere triangulation so I say really if anyone ever finds themselves like me caught in the middle that's a massive red flag and basically get out while you still can!
I got caught up in it and now my feelings are ambivalent I love my husband but I can't really relate to him much and his behaviour at times has been incredibly frustrating and hurtful.
Now I am willing to admit defeat because I have got him to recognise that fact (very recently) and he's finally admitted he was wrong and that's something he has never done before.
So life goes on....the pain has faded things have calmed down he's not as egotistical as before thank god and he no longer has to defend himself because he admits now not all criticism is a form of attack!
Yeah so I'm ok I feel like I have been through a lot but tbh I was so naive when we got married that maybe I was due a bit of a reality check! (Happens to the best of us).
You live you learn...?
Funnily enough I used to think if he had an affair I would actually be relieved because living with him was too intense and it would take the pressure off me?
Now I look back and realise that would have been selfish of me! Why because you should never offload your problems onto another person?
If he had done that the whole triangulation pattern would have started again and another woman would have been in my situation and most probably would have got hurt?
So it's good to end things and it's good to accept things are complicated but when you grow up s bit you realise that you just don't need the drama it's not worth it!
In regards to his former girlfriend I realise I sounded critical at the start of the post probably because I felt like I shouldn't be the one that she went for!
Now looking back I feel like we both were (willingly fooled) because we both wanted to get someone who looked easy to have but actually was difficult to get to know because he has always been afraid of intamacy?
That's the real problem isn't it Mr or Mrs hard to get?
Whenever any of us find ourselves attracted to someone hard to get we have to know that our strings are being pulled and we are being manipulated and for me that's the real horror.
You think you are free but someone is playing games and guess what that turns out to be no fun at all!
So those who are elusive lie or tell stories or make themselves the hero or heroine of a narrative are always going to be unmasked eventually as the narcissists they surely are.
If anyone finds themselves like I did falling for an idealised image please forgive yourself because it's a mask that others wear and sometimes it hides a not very likeable person underneath it all.(and they know this and that's why they are secretly afraid).
They are also scared of being found out I should know it took me 21 years and that's 21 years I could have nurtured and supported myself!
So ultimately although it sounds really clichéd the best thing is to have a love affair with yourself if like me you find yourself lost or lonely or lied to?
That's the only thing that can help in the long run!
more fool her!
also there’s obviously different degrees of cheating, if my fiancé kissed someone drunkenly at a party I wouldn’t be booting him out but if you consider how many opportunities there are to stop and think ‘hey, maybe I won’t completely destroy my partner’s trust in me’ when it comes to meeting someone, planning the details of an affair/where you’re going to meet etc etc, actually going there and going through it…damn straight I’d be out with the ‘theatrics’ and it has happened to me before. 
