And where are you amongst all of this?

Look hun, it feels as if you are pointing the fingers at everyone else in the house and are yet to think about your part in it all.
It seems you are more committed to fault-finding with sds than anything else. I've not seen you write anything positive about him, I can only imagine what it would be like having to live with someone that picks at you or give a constant air of disapproval. Can you imagine that for a moment? He is still only a kid and motivation isn't born from underconfidence.

You have the chance to be a very positive role model for this boy - do you expect DH to be a good role model to your children? Is is fair to expect the same?

Skeeta brings up so many great points - you have put yourself in a position with someone you know and admit you have feelings about, you have crossed the line with him....I'm not sure why you are so insulted DH accuses you of having a fling with him - he isn't far off the mark after all.

Maybe have a longer look at yourself and your own behaviours and take responsibility so you can fix this marriage. If that's what you truly want.

xoxoxo