Well Disney never sagte BOLT and Mittens are a couple. But if they were I think it's because Mittens showed BOLT how to be a regular dog and Mittens is his friend. But that's what I think.
They are not in love, some people think it, but they are not, there just REALLY SUPER DUPER GOOD FRIENDS! Don't get me wrong, I have seen the bolt Bewegen like, over a million times, they have never done 'the look' before, (that means the Liebe look, were they Zeigen Liebe in there eyes) and here is a picture i made of bolt:
