You should just move on. As hard as it will be at first you will feel a lot better for it.
I have been following this discussion for a while now and have some thoughts for the OP and an experience to share.
I can understand how you feel because I once lost a very good friend and mentor in much the same way although this was before I got involved in martial arts. The issue was not mine, although I was made to feel like it was. It is very difficult for a woman to have a close friendship with a man and not have people think inappropriate things about the relationship. Especially if that woman is single. It is especially a problem if the man is married and his wife is not also a good friend. In my case I tried to become friends with my friends wife as well but was rebuffed and rejected. When I discovered that she actually thought that I was interested in her husband in that way I tried to make it clear that this was simply not true. I am a widow and have no desire to be involved in another relationship in that way. I have always been pretty open about saying so. I like my freedom and am not willing to give it up along with many aspects of my life that a relationship would impact.
To me, my freind was like an older brother and our conversations and friendship really helped me to grow as a person and to start to find some balance in my very confused life. The loss of that relationship was painful and difficult. But I moved on...eventually. And am much better off for it.
The way I see it, he did what he had to do in order to take care of his marriage. And really that had to be more important than our friendship. The issues that they had in their marriage were not of my making although perhaps my presence brought them into the open. It wasn't however my fault. I still miss having him in my life but I have made new, and in many ways better friends. Friends who see me for who I am, and don't assume that because I am a single woman that I am out chasing every nice guy I meet.
I have a pretty close relationship with another married couple now, but in this case both of them are good friends and neither of them is an insecure and possessive spouse who does not trust the other to have close friendships with the opposite sex. It is refreshingly uncomplicated.
It is a sad thing that here in 2013 an adult woman can still not have a friendship with an adult man be he attached or single, and there not be those who suspect her of being romantically interested in him. Even people who consider themselves more modern in their thinking and more open minded will still go down that road. Life is too short to waste any of your time with people who don't see you for who you are and accept that. If you constantly have to explain yourself to your friends in order to keep from loosing their friendship, you need better friends.
Stop wasting your time trying to hang onto something you can't have.