Totally agree with post above - for all they have totally different personalities and interests, they both seemed serious about the relationship. You do need to wonder whats gone on behind the scenes for the sudden breakup, not to get personal but I've been in a kinda similar situation, (ex) partner of 2 years jumped ship to be with a friend in the middle of a house purchase.
They basically came out a few months later & said that while they had been committed & happy in the relationship, the fact I was financially able to purchase property made them feel very childish & unfulfilled as they weren't in a similar position, so inadvertently a wedge was driven between us over nothing, while the friend was in a more similar position to them & was able to trigger a feeling of being 'young' and carefree. This was 2019 so I'd have been about the same age as KL & G are now I think.
Doesn't make anything that's happened right, or portray either of them as the better person necessarily, just to show that really random things can set people off in different ways. I wouldn't be surprised if KL getting the dogs and house IS the thing that triggered the sudden breakup, but rather than in the way we first thought (grace not wanting commitment), that it could have been disheartening for grace to be with someone with a very clear and planned out view of what they want in life, when she was still so unsure.
Just my 2c, anyway.