Hello, my name is Greg.
I think I am reading this correctly. Your BFF is the man who married the woman that you are not able to be friends with but you want to maintain a friendship with the BFF but not see the wife, correct?
That can be really difficult in these situations as the BFF will see you as not accepting him and the wife will often do what she can to undermine the relationship (which is somewhat understandable if she feels you might be trying to drive a wedge between them).
Honestly, the only way I usually see these issues resolving themselves is through honesty with your BFF. You need to sit down and have a real discussion on this and be ready to not be defensive but listen to their point of view as well. You must know going into this though that your relationship with your BFF may have to be more limited, at least for a period of time.
Remember that even though you might have to pull back from the BFF for a while, that does not necessarily mean that it would be long term but maybe a "cooling off" period is needed - you are the BFF and she is the wife which causes him to be in a bad position as the two important people in his life are not getting along and he is being pulled from two sides.
All the best to you in this situation. I wish there was an "easy" solution to this but there is not. Be honest and open and you have the best chance of finding a medium in this situation.
Please be sure to rate my response positively so I receive credit for my help today. :)