My friend, Rodeo Man has said it, I'm afraid you are a sex addict. Doesnt seem to matter how much you love your wife/gf.
I went to a shrink last year to get some help and was told the only cure was to join in SLAA (Sex and Love Addicts Anonymous) meetings. Serious! I didn't go. Not sure if I bottled it because I didn't want to bump into anyone I know. I actually thought I didn't really need to listen to other peoples problems or talk to a group about mine and that I could just deal with the issue myself.
Anyway, the self help route isn't going all that well :-)