How do i stop getting a bonner when i make outt?

You don't: You want to get a boner / erection when you are close with somebody that you like in a romantic way. She won't be offended. In fact, this must happen if you are going to be a father someday. If anybody has told you it's wrong to get an erection like this, make a mental note that person is a fool or just not to be trusted. And congratulations on your changing body and on growing up.