Is being lesbian/gay bad?

Well, as someone who identifies as gay, I'd have to say it's neither bad nor good... It just is. People have different tastes, they're going to like what they like, no matter the reason. My main concern(s) with pretty much any preference/orientation/identification are as follows: 1) Does it cause harm? 2) Are any involved parties willing, and able (both physically and mentally), to consent?

That said, your friend's sexuality is just a small piece of their whole being. They're the same person that they were beforehand, you just know a little more about them now.