I'm sorry, I don't have a lot of good tips for this. I would try even harder to avoid sharing these insecurities with your girlfriend. You know that they are not rational and not really about her.

The only caveat is when you are worried that if you do X, she will think Y. Like if you decide not to go to the game and instead sit around the house with her doing nothing because you think she wants quality time... but if you ask her about it, it might turn out that she wouldn't be bothered at all if you went out.

Do you have a close friend you could talk about this stuff with, as an outlet? It can also be helpful (I find) to find out how other people think about certain situations-- like what do your friends think is 'enough' interest as opposed to 'constant' interest.

Some CBT techniques may be useful as well.