YES you have a right to set boundaries, even now. The person you live with also has a right to negotiate things with you that you might not like, but that is up to you to figure out what is OK and work to come to a compromise together.
His behavior you've described? Not OK
You not wanting to have sex with him but having desire for another partner? OK, as long as you are trying to improve your intimacy with him.
Finding healthy ways for him to get his libido massaged that doesn't hurt your relationship? OK
Actively seeking couples counseling to see if you can have a more happy intimate relationship if you both want one - ALWAYS OK
Him acting out because you don't want to have sex with him as often as you do with somebody else, so over-jumping into an "important" relationship with some random FB contact and being an inconsiderate prick about it? Not OK.
So if he wants to get involved with this new person? Sure!!! but you need some boundaries and I'd say if you haven't read Opening up by Tristan Taormino, what are you waiting for? (Plenty of other good recommendations on the book/website sticky) The whole "well I have another partner so I guess you can do whatever you want or it isn't fair" is not necessarily helpful, it neglects the fact that it's not nice to treat people you love badly, either on purpose or because you're acting out because you're hurt.
Happiness will never come to those who fail to appreciate what they already have.
Last edited by Anneintherain; 07-20-2012 at 06:39 PM.