Well, here are some facts.
Justin Timberlake is currently married to actress Jessica Biel.
Justin has said during interviews that he is straight.
Justin said that he has a lot of gay friends.
Justin has said that he supports gay marriage. (On New York legalizing gay marriage: "I was stoked. I mean, I was stoked that that happened. I think it’s just…we’re people and we’re different, all of us. And we should be using our differences to bring ourselves closer together. You know? Not be afraid of something that we don’t know. Like Mila said, and you know, I have a lot of guy friends who are gay. Two of my best friends are a couple, and my conversation with them is, like, it’s unfortunate that things take a while to progress like this, but it was a great, great victory for equality."
In other words, I think he's straight. It's nice that he's so vocal about gay rights.