grief is totally personal, and i believe youve been through a certain amount of it.
i think your recent relationships are a way of protecting yourself, and being in control of your love. you get with these women, who you know you have no future with, and that is easier to cope with. youve been terribly hurt, by first of all losing your fiancee, and then learning of her infidelity.
your initial reactions are down to shock (ahh, what a wonderful thing shock can be!)
you just have to be able to trust people enough, to let the right person in again. thats a tough one, because you couldnt get closure. you couldnt confront her about the infidelity which left so many questions unanswered i imagine.
im not an expert, but i have done my fair share of grieving, and although i cannot help you in any real way, i truly wish you the very best, and hope you can move on and enjoy life again, the way you deserve to.
and just a quick note, congratulations for conquering your dependencies. that really is commendable, and i can again empathise with you on a personal level.
big hugs for you, you sound like a lovely person