Yeah I kind of get the idea that maybe they're really socially awkward and/or backward and/or literally don't understand things or can't cope very well, especially regarding one-word responses and the like, esp. if they're not that way online and they went home and SAID they had fun. Maybe they DID have fun, or they were confused about how to interact with other people.

My ex-bf and I made a deal that if /i/ went to visit him, he paid for everything, and if /he/ came to visit me, I would pay for everything. Like, "my turf, I'll take care of it!"

That said have you tried TALKING to your friend, OP? Communication is really important and you should tell them in a private message that you are concerned because you didn't feel that they were having fun at all and so on.

My friends I've met in person mostly can't get me to STFU.