I think that since you are just starting your marriage, and you already have to deal with grief 3 times, plus infidelity, it appears as if she thinks happiness is elsewhere. The truth is, it isn't, life goes on throwing many punches, but some people don't get it, that it's the anwavering support through the bad times what matter, not just the highs of fun things, parties, sex, the excitement to kiss someone new etc. That doesn't last, it's what happens afterwards that last, but some people simply don't get it.

I know you love her, I can feel it in the way you write. I think she has her eyes set elsewhere and there is nothing you can do. I'm in the same situation, husband fell out of love and is divorcing me, even though there is nothing wrong in our marriage. He is the problem, and I enabled his bad behavior by forgiving him, not asking for much, making do with very little... Instead of demanding what I need as a woman, spouse, mother. That was my fault, I did not see that my efforts were reorocicated, it was all about him, whole I trained behind.

You deserve EQUAL give and take. If she is not willing to give, then you are alone in the marriage.