I second this.

It might not be the solution, but I think the attempt you need to make is just that, get into the office full-time, join breakfast and lunches and whatever else activity is there, and try hard to accept yourself that you're quiet (at the time being).

I've felt like this at times, like I don't belong, felt bad that I'm the weird one (I totally am), but I've forced myself to be there, to participate, not to feel further outcast, and it has helped every time.. I'd go so far as to say that the more disconnected or outcast I've felt, the more I've made a point of being there, even if quiet.