I think it's not wrong to have a thing for my gf's sister and mother
So who do you want to be in a relationship with then?
I don't feel like I want a lasting relationship with any of them yet. Just hooking up.
If you don't want a relationship, you should be honest with your girlfriend so that she knows that you are not in it for the long haul. And that you have feelings for her mother. Then she can decided if she is okay with either.
Well I told her. I'm single now and dating around.
Now that you are dating around, you should make it a habit of letting the people you date what your expectations are. So that you won't waste either of your times.