I guess I just have some questions...

Is he an introvert? Introverts energy essentially gets drained by being in social situations, so maybe he's trying to recharge. I'm an introvert myself and I don't really want to go very many places outside of the ones that I already have to go to everyday.

If he's not an introvert, has this been going on since you've known him or is it a recent development? Because that could potentially be some sort of warning sign.