Is it normal that someone gets bitter when you're happy with other people?

hmmmm...maybe it's not that..maybe she wants you to be happy for sure, but kinda freaks out when she feels she can't make you happy? You just said for you it's ups and downs..so when you're around her, sometimes you're happy and sometimes not. You also said you try to get out of your down mood to be happy with her, right? Maybe she doesn't understand it this way again. Perhaps she sees that she is not enough or that she doesn't have a hold on you..maybe she feels it's her fault..get my point? Sometimes you need to feel you make a positive difference in someone's life, like they need you. If you're not needed, that will make you feel insignificant, that's probably why your girl friend is bitter.

So, if you are the one who can see the whole picture..and like you said it's not about her, it's just that you are not the "happy-all-the-time" kind of guy, then you need to assure her that she is especial too. Try to let her see that you appreciate having her in your life and the things she does for you. And don't be negative around her most of the time. Try to be cheerful a bit. It will make you both happier :)

not normal it seems she wants to be the only person to make happy, warn her that you want to spread yr wings and socialize, tell her she is making you sad by being angry and you dont like that and if it continues you 2 will have to part, give her time to digest this and change

That shit happens to me all the time.