Most Helpful Guy
Simple. You ask him. And you ask him now. BTW where's his fiancé in all of this? You didn't mention her take on your relationship or him being with you and talking to you even though you're giving the best man speech. Will your relationship with him change once they say I Do? My guess is yes. It seems wives have ways if pulling in the reigns from that moment on. They can may life pleasant, and they can make life a living hell. It's not easy to tell which it will be from the beginning.
From what I read it sounds like the two of your were made for each other. I'd give anything to be back in that kind of relationship. They're few and far between. If your boyfriend and his fiancé don't have the connection the two of you have then his marriage will be, let's say, less than ideal. No, let's say miserable. I married someone I got along well with. Relationship was good but not like yours. 25 years later...we've both been miserable for almost 10 years...
Ask him. Ask him now. Is she really the one? His soul mate? Or are you the one? The one he knows he wants and needs to be with? It's a life long commitment. Don't let him make a mistake. You may not be here when he comes looking in 10 years. Make the right decision now for the all right reasons. I was too stupid to make that decision for fear of hurting someone. Now the hurt involves more than one. Talk to him, please. Best of luck to you both.