Do you believe in monogamy?
That's a hard thing to say. I personally would rather have only one partner at once but I can't really tell other people how to run their life unless they're being abused.
So short answer: I don't really believe in it. I tend to say "go with what makes you happy" if that means having 3 boyfriends at the same time, so long as no is being neglected, that go for it!