Hello Sarah,
You have some issues with your self esteem if you are turning down dates because you think that when a guy gets to know the real you, he’ll be disappointed. He says he’s having relationship issues with his girlfriend. This guy is part of this relationship and if he doesn’t believe in relationships any more, then he doesn’t believe in himself.
If you get the chance, it’s quite in order for you to say that you don’t want him flirting with you while he’s still with his girlfriend. Also, avoid him when he is drunk. Getting drunk on a frequent basis is a sign that he is not handling his own issues very appropriately.
There is no reason for you to leave the group unless you are feeling uncomfortable in this situation. If it really does depress you, then leave the group. You can leave him your number should he ever want to contact you.
Best Wishes
Peggy