Break ups are rough, and when one person moves on and the other doesn’t, it’s even rougher. 😳 I’m really sorry you’re hurt. The thing about relationships is that just because you’re dating someone, or even living with them, doesn’t mean they may not meet someone else they want to be with. In fact, people who are married with kids for decades find themselves in these situations, too. That’s not to say that there aren’t plenty of happy, healthy, long-term relationships — there are — but if the two of you weren’t compatible, and he found someone with whom he wants to share a life and a marriage, the rejection stings, but the reality is he’s not YOUR Mr. Right. Someone else is. 😉
Cheating doesn’t happen in a vacuum, unless the person is a chronic cheater, and it doesn’t sound like that’s what’s going on here. Something in the relationship you and with him left a vacuum for him, so that when he met this other woman, she was the one for him — even though he’d been with you in a committed live-in relationship. The good news is that you weren’t married, didn’t buy a house together and didn’t have children, so while it’s still painful to recover, you were able to limit your losses.
Now that it’s been a year since the break up, it’s time for you to move on. I know you’re probably thinking that you’re too hurt to do so, but the irony is that the hurt will fade away when you start dating again. Take care of yourself in every way, and make the effort to start dating again.
I hope that helps and that you feel better soon — let me know if you have any more questions.