Re /m13:
if I push buttons that give someone who's plugged into the right interface sexual pleasure, am I performing a sex act?

Depends. Does it feel like a sexual act? If you do it unknowingly,
I'd say it isn't sexual. If you are IMing someone with erotic
suggestions that get the recipent off (the "right interface"
there being the written word) then yes.

Am I "cheating?"

There is an easy test that answers this question. Would you
feel uncomfertable telling your primary partner about it?

If that person's the same gender, is it a homosexual act?

Only if you let it be in your mind.