My boyfriend and I have been dating for 5 1/2 years and we act like a happily newlywed couple. (I only say this because everyone assumes we're married!)
We keep our relationship alive by sharing hobbies and going on walks to department stores together! We also plan dinner dates. It also helps that we are both working now and don't see one another all the time. We don't do everything together, either. There are things he will do that I have no interest in doing. We have our best and supportive talks when we go walking. There must be something you can do with your girlfriend where conversations can come easy.
If you have to, you can talk to her about masturbating and see if she's okay with you doing so. Sometimes libidos don't match and you have to figure out ways around it.
Good luck!