Why does it matter if he's gay? What else do you know about him, like his political leanings and his stands on various issues? That's what's important when choosing a running mate.
Gayness is a polarizing force like abortion - either you defend it or you don't, and it can swerve the voting curve nicely when played out to be an issue. Personally, I don't care if the guy is gay as long as it doesn't affect his politics. The only reason I can think of why it's important he's gay and he's in Massachusetts is that their education system that already teaches "fisting" and recruits for gay sexuality will not be challenged if he has any say in the matter. Therefore, it really doesn't matter what else the guy says or claims to stand for. MA has that reputation, as other states have other reputations.
As long as he upholds the Constitution and "services" his majority constituency, they can all live in the same putrid stench. But the kids shouldn't have to grow up being forced into sexual ambiguity while they're still too young to understand the politics.