Why do i feel left out?

You should let them know how you feel. Maybe they're not the kind of friends you really want to hangout with. Your probably hanging out with them for another personal reason. If I was you, I would tell them my feeling, and if they don't agree or not willing to make you feel comfortable, then you need you some new friends. You deserve to be happy, friends can last a lifetime, and are one's you should be able to tell everything to.