Right I'll just get down to the point, I've been with my girlfriend for 3 years now. But only recently during sex I penertrate her with a 100% erection, but after a while it goes down to around 50% or even less while we are still having sex, this is very confusing for me seeing as she is a very attractive girl, and I was wondering if someone could help me find out while I can't stay erect while having sex with her