I am so sorry you are going through this. The passage of time is the only healer in all honesty. You need to look after yourself and appreciate, and find time and ways to enjoy in, the smallest things. Don't get back in the dating game for a while - give yourself time to grieve and heal.
I'm a great believer in things happening for a reason; you will look back in time and see that if this hadn't happened then it would have lead you to --- what's coming (and it will be magnificent).
For now though, self-care must take priority. I know it's hard - I've been through this too, and just wanted to curl up and die if I'm completely honest - but you will get through it. Engage in a new hobby (even just learning something new online), and if you need to talk, try to do it with a counselor or online telephone service dedicated to counseling ... try not to talk with your friends as - and again this is from personal experience - it will tarnish your relationship with them.
Much love to you. You WILL be okay, just know that.
Edited to add: One thing I did find helpful: Hypnotism. It's not for everyone, but I just could not get him out of my head and developed a very unhealthy habit of psychoanalysing everything I'd said and done while we were together that might have caused him to dump me. The hypnotism 'sort of' made me forget all about him. I still had feelings of sadness and felt like I'd been kicked to the curb quite literally, but it helped severe the blow. I suffered from a lot of childhood emotional trauma that tended to overflow at this time also - it's all tied into the fear of abandonment - so it felt very much like my world had come crashing in and I had nothing to live for. I also ended up changing everything I could - new city, new job, new haircut, new dress style - I reinvented myself which psychologically helped me move on from being the victim of something that was beyond my control.
Ain't that the truth?! Years later I realised that if we were still together I'd be married to Frank Spencer! (Not only did he bear a strong resemblance to this character, but also many, many traits)
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Oh my goodness, that is just so hard to read. I can't imagine how you are feeling.
Please don't feel that you have nobody - plenty of people on here care about you.
If you are able to, perhaps ask if he is open to having a frank and open discussion with you about his reasons for leaving? It might be that whatever those reasons are, it is salvageable - but you will have to insist that you both work at things, and that includes him not leaving like that again.
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