It just seemed he felt pretty comfortable at your home which I think is a good thing. He didn't really do anything that would cross the line between two dudes.
You could probably take his offer and go visit him if you like. I assume you love your GF so my guess is he won't be able to seduce you to a threesome with his gf because that's straight cheating on your gf.
You could even bring your gf. Maybe this is the start of a wonderful friendship :)
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