I'll move the topic to Women's Issues,
since he clearly wants female responses
primarily.
As for my opinion: Your girlfriend needs
to open her eyes. Many people masturbate
while in relationships. She shouldn't get
jealous. As someone else said, it's a heck
of a lot better for you to masturbate than
to say, cheat on your girlfriend! Why
don't you tell her that? She might not
like to hear it, but then again she may be
at an age where she still needs to develop
some maturity and understanding.
Heck yeah it's normal. I masturbated even
when I was dating someone for two years
and engaged to him!! I still touched
my'self when I was alone

Masturbation is a
very personal thing, and it is not
"self-sex" in any sense. It is different
emotionally and physically from real sex.