Hi Only Human. This exact situation happened to me. An ex of mine that I was head over heels for wound up marrying the girl he cheated on me with. It's very painful, I know, so my heart goes out to you. They also had 2 kids together. Really rough to hear even years later. Eventually they wound up divorced and through the grapevine I've heard he has since been through 2 more marriages. So as Open Eyes said, you can't know that your ex will live happily ever after. He most likely still has the same problems now as he did previously. And we all know too well that people on Facebook mostly reveal the positive aspects of living, not the negative.

2 years isn't really all that long for getting over heartbreak. It will slowly keep getting better. Be gentle with yourself and try not to compare yourself to him. You do deserve love and happiness too.