This is a chicken-and-the-egg situation. You're saying you can't do it this way because you don't have self-respect and confidence, and I'm saying you don't have self-respect and confidence because you're allowing this to go on this way.
Your boys are at VERY formative ages for how they are going to deal with the opposite sex in relationships and, eventually, marriage. What traits do you want to instill in them? You've certainly taught them love, and forgiveness, and you're to be commended for that. But what about boundary-setting, fighting for what you believe in, and taking a stand?
You need to know something about me: I am NOT a "tough guy." In fact, quite the opposite. I am a romantic, and a lifetime "pleaser", "rescuer" and "Mr. Nice Guy." I had to LEARN how to do this stuff, it did NOT come easy or natural to me. I STILL have to work at it -- a LOT.
My suggestion would be to pick ONE other area where you might be able to draw a boundary, like you did with the "I will no longer tolerate you disrespecting me by talking about OM around me." Is there something else that really eats at you?
Finally, I do think there was something that helped me steel my resolve, so to speak, and that was how actively I gathered intel about what my wife and her boyfriend were doing. Seeing and hearing the things that I saw and heard made it MUCH easier on me to do the difficult things necessary to take a stand for my marriage.
