My advice is don't worry about Jerry, he's a big boy and can take of himself.
I think your "problem being faithful" should be your main concern. Given that you are young and open to a range of sexual encounters, why are you worrying about having serious boyfriends at all? It seems to me that right now you are into partying and having fun.
I don't see anything wrong with that...in fact, I've always been so serious about relationships that I'm a bit envious of you, to tell the truth!
So, I guess my advice is, tell Jerry that you are not really into being his girlfriend, that you really like him and would love to hang out with him, but that you are into being just for yourself right now. I think that's perfectly acceptable.
If your friends are judgmental, that's really their problem isn't it? You are comfortable with who you are...you said you had no regrets about having sex with Bryan.
When you are ready to be more serious and more monogamous it won't feel like struggle, it will feel like the right way to be. Don't force yourself into other people's expectations. But, I hope you are using birth control and are practicing safe sex.
Honesty is Better Now than Later
Yes, Jerry's feelings might be hurt, but your honesty is better now than later. If I were him, I'd much rather know what I was doing with you and what was really going on. Wouldn't you?