Some times people are simply better off not together in all aspects. I know this sounds defeatist but not everyone can be compatible in a healthy way.
You're tempting fate with the massages and we both know it. If you are truly committed to maintaining the relationship with your husband I would strongly suggest you do pull back from this friend for a while...only because you are admitting you want this so bad and don't know what you will do.
That being said, you and your husband have to look at the reality of your situation. You aren't happy in the compromise you have. He is not either. Both of you have been "putting up" with it to keep your relationship together. How long can you be healthy holding back? How long can he be healthy holding you back. This is tough for both of you. He has to know how draining this is on you and you have to know how draining this is on him. Speaking from the perspective of the person who holds my partner back, it is very draining to feel that you are always putting your weight against the damn.
No matter what both of you decide you need to be fully prepared to accept the responsibility for your actions. If he holds you back from something you really want he's got to accept responsibility if you cross that boundary.
If you let this relationship exceed the confines of your boundaries then you have to accept the potential fall out as well.
You're in a tough situation. I hope you find your way in this.
Playing the Game of Life with Monopoly rules.
Monogamy might just be in my genes
Poly Events All Over