Girlfriend?

Alright guys, this may be weird to some of you so if you're religious or against same sex relationships I don't want to hear it. I have a BOYFRIEND and we've been together for 3 years. But he lacks in the foreplay... and it really sucks. Sex is okay but it was nothing like the time I had sex with a girl, my boyfriend was there and even watched. He did not however touch or join in. I'm openly bisexual and he knows it, but recently I've been thinking about having a girlfriend to have "longer lasting fun" I guess you could say. I have not brought it to his attention as I think he might get mildly offended... should I? Should I ignore my sexual fantasies? I know that I want him as my forever partner but a fling with a girl doesn't seem that bad... opinions?