I've been with my girlfriend almost a year know. I've been active on the forums here but I've never cheated.
My girlfriend always got on well with my cousin who stays with us a couple times a week to save her driving from Gorey to Dublin every morning for work. A few weeks ago they got together and asked if we could all have a night of fun together a threesome. I've always wanted a threesome with 2 girls but not with my own cousin so at first I turned them down and wouldn't. But being a guy I crumbled one night when they started kissing and undressing each other.
It was a great experience and I'm not ashamed to say we've done it more than once since then.
Last weekend while we were together I suggested that next time we invite another guy to join us. My cousin loved the idea. I'm bi she was the only one who knew before last weekend. I've suggested a guy who I've had sex with before that knows my girlfriend well, and she went crazy saying it would be weird and we shouldn't invite a guy into our bed. I asked her why it's OK for my cousin to join us and not another guy who we both know but are not related. She replied that being with a girl is safe and we don't know what this other guy might have and she wouldn't be comfortable watching me with another guy. I suggested she can pick a guy she trusts and she flipped out and went back to her parents that night. She came back Monday. But hasn't mentioned anything about and last night went into my cousins bed and had sex with her. I'm furious now, with her and my cousin and seriously considering sleeping with another guy.

I don't care if it's considered cheating, she seems to think it's ok for her to sleep with the same the same sex so why can't i.