In my humble opinion, the issue is not whether the behavior is "normal" (i.e. whether other people do the same thing) but whether you feel uncomfortable with it. You have indicated that you do. Specifically you have told your husband that you are uncomfortable with his facebook contact, and that he appears to have continued online contact with this woman. Is he disrespecting you? To the extent that you have told him how you feel about this behavior and he has continued it, the answer would appear to be "yes".
Now for the big question: What do you want to do about it? I have learned that if I am uncomfortable with a situation, I need to set a boundary and enforce it. For example, my husband has some elderly relatives for whom English is not their first language. They will often lapse into lengthy conversations in a language I neither speak nor understand, leaving me out, which I find rude, and, more importantly, I feel uncomfortable. I said something to my husband. I was not happy with his response. So I decided that I will not stay in the room when that happens again. Now, when it does happen and my husband sees me start to head toward another room or out for a walk, he switches back into English.
What can you do when your husband's contact with other women leaves you with an uncomfortable feeling? Some friends I know who go to gatherings at the type you were at will leave because they do not want to subject themselves to such discomfort. Some will step in when such interactions are occurring and say something. It's all about what works for you. Yes, your husband will likely give you a hard time. I have learned I do not have to explain or defend anything in this regard. All I say is " I cannot be subjected to this" or "I cannot live with this" or something similar. It is then up to the other person to decide how they will respond. The good news for me is that I have choices as to how I will respond and that I do not have to simply "take" the behavior and stew over it.
The computer is a tougher one. My husband's internet activity got so out of hand, I installed a filter---not because I intended to control his behavior, but because I will not live with smut coming into my house in any way. I am not necessarily suggesting you do this. I am merely telling you what I ended up doing. In my humble opinion, you do not need to get into whether what he is doing is "right" or "wrong",you can simply let him know that you are uncomfortable, and that you therefore will do what you need to do to address the discomfort. If he does not like what you decide to do, he can change his behavior or deal with your response.
One last thing: I would NOT go out and do the same thing to get back at him. If, as you say, it goes against your values, then that would be the worst thing you could do, because then you give up you to make a point to him that he probably will not get anyway.
Hope this helps. If not, feel free to disregard it. Good Luck!