"But I am not sure if it is okay to discuss my feelings about it because I know he is hurting too, he was married to her for 12 years!"-Brunetteangel103
Resolution in a situation comes more smoothly when a person feels they aren't alone in their situation. Perhaps you can relate to each other in how you feel. It can't hurt to ask if it's ok if you talk about your feelings with him. A straight forward question, since you love and miss her and may feel betrayed and angry as well. He may find he relates to you and you can work through the mutual feelings together.
I agree with Danny here, transparent honest communication rarely goes amiss.
The wife is going through a lot now too, perhaps a show of support, acceptance of, and happiness for, her new relationship may ease the tension between you and renew a friendship knowing that you harbor no hard feelings may help ease her mind.
This can't be easy for her. It sounds like exclusivity was the new love's idea. Is that what I read, or were they mutual on this? Knowing that she has hurt both of you is probably present in her mind and may bother her but her main concern now would be to move on with the choice she has made.
Will there be a custody issue? Certainly that must be on everyone's minds and no one easily walks away from a 12 year or even a close two month relationship without some regrets.
I hope you find peace in this situation. We are here for you if you need to talk about your feelings. Let your R/T friends outside the situation be there for you as well. I don't know what your support system is like but use the resources you do have. You aren't alone I would imagine many if not all of us have had something similar happen. Support him, Support her (if you can and she is open to that in a platonic way) but don't forget you are as important in this equation. Take care of yourself, if you don't you won't have enough to give. This is a grieving process and it takes time so be patient with yourself. (((hug)))