I suggest you talk to your girlfriend about it, and see if she wants to try other things too. If this isn't a loada horse....stuff, that is. You're clearly a swinger which, other people of EoFF, isn't a bad thing (though I don't like the idea of it). But, unless both partners do it, that is cheating. It's not considered by some to be cheating, it just is cheating. No two ways about it. It's the old "I make love to my girlfriend, but have sex with other people" thing. Nothing wrong with it as long as it's two-way.