Don't give up! In our guild, at the beginning of the evening the president always asks if there are any guests. That gives visitors a chance to stand up so that members know who to welcome. I know when I first started going to guild, I didn't know anyone.
Next time if you see someone else sitting by themselves ask if you can sit by them. Another hint, ask questions, like how long have you been quilting or what's their favorite tool? Too many times we get hung up on not wanting to bother someone else.
We all know how kind and generous quilters are so don't give up!