I can only facepalm very hard over the original poster's attitudes.
"It's not cheating if it's lesbian"
"Can I watch?"
Seriously, cheating is cheating. And no, most lesbians are not going to let you watch, the same as most hetero couples aren't going to let you watch. They are human beings, not things there to entertain and excite you. There are plenty of movies out there for that.
Now, me personally, my girlfriend DOES see other people. Men and women. And tells me about it. I am okay with this, as we have an open polyamourous relationship. She is also perfectly okay with me seeing or dating other people. So for me, my girlfriend can't 'cheat' on me, unless she's hiding things. It doesn't bother me in the least that she sees other people, in fact I find it kind of fun and makes me happy for when I can't be there for her.
However, if I were in a monogamous relationship with the expectation that neither of us saw/dated/slept with other people and I found out that my partner was going behind my back... I would be hurt regardless of the gender of the person they saw. It's not a matter of who they were seeing, but the fact that they broke the trust we had that makes it cheating.