I wouldn't worry too much about it man. I do it at least 3-4 times a day wether i'm currently dating someone or not. I've even done it when my girl was passed out next to me. I'm no doctor but this just seems like normal male behavior, but I could be wrong. Are you a virgin? If so, did you have the 15 second problem with her? I ask because I last a lot longer with a girl than by myself. I obviously enjoy being with a girl much more, but I don't want to be done untill she is. I'm not sure how, but I've learned how to do this. I'm not sure but I think there might be some type of treatment for the ol' 15 second problem. Also, using a condom could help a lot as you can't feel nearly as much. I can't even finish when using a condom, which btw you always should. Anyway, good luck.