Girl - My boyfriend and I are thinking of having a threesome. Is that good? Bad?

There's nothing wrong with it. But make sure it's what you want to do first.

Yes, of course. As long as you think your relationship is strong enough, that you are liberated enough sexually, and that jealousy won't be an issue. I have an ex-girlfriend who became a lesbian and often, to have sex, she has threesomes with couples having a bi-curious female (she doesn't sleep with the male). She told me how common it is that the male seems fine with it, but then problems start to appear.