Wow, that sucks, OP. Sorry you had to go through that. Social anxiety or introverted personality or not, that's no excuse for what your "friend" did. I'm introverted and socially anxious, and meeting new people is always a challenge, but that is not a free pass to leech off others or not thank them. Even if talking about money was awkward for them or they found it difficult to find the right time to thank you, they still should've tried. (And from your secret, it seems like they didn't, not during the visit or after it.)

Probably the best thing to do would be to talk to them, tell them how you felt about the visit and ask them if they realize just how rude their behavior looks like, and depending on how that goes, sever the friendship or try to mend it. Best of luck, OP.