I think it is shameful and tragic that he is using your children as pawns to try and maintain his control over you. I think counseling may be a good option for your boys, but I would first suggest you find a counselor that you are comfortable with and have some sessions of your own. You may get some helpful feedback and suggestions.
I have found that when children act out, there is usually something bothering them. And it usually comes down to fear. Maybe they fear he will take them? Reacting to my children from a position of power or authority only seemed to make things worse. When I ask questions and listen to their answers, then they calm down. That doesn't mean I give in to their wishes, just that we communicate better. I am the parent, and I still make most of the important decisions. They don't have to like it, and they are absolutely allowed to have an opinion about it. They are not allowed to treat me with disrespect and I don't treat them with disrespect. Your ex is treating you disrespectfully in front of them and they should understand that it is not okay. You can't make him stop, but you can instill values in them so that they do not grow up thinking it is okay to treat others that way.
As far as dating goes, I made sure my kids knew I was making new friends. Both male and female, and just because I was going out didn't mean it was a 'date.' And just because I went places with a person more than once didn't mean he was a 'boyfriend.' And this is true. I am not in a place right now where I want another husband, or even a live-in companion. Just someone to go places and do things with. Luckily, I have found someone like that and there is no pressure for anything more. My kids are fine with it, too. But then again, my ex is not acting like a pathetic, immature jerk, either.
So sorry you are dealing with this.
L