Crikey! Gautam's got a sailor in every port,
....I'm WAAAAY jealous!!!
OK,..2 cents from Jerry,...
You've got a serious guy in Prague, a "just for fun" guy nearby whose roommate you want to jump on,....hmmmm,..there's nothing like putting some effort into complicating your life, and you're doing a damn good job of it!
If "I" knows he's not in a serious relationship with you, then I'd guess you should check with the roommie,..and make sure that there's something there, then mention it to "I", BEFORE anything happens.
Honesty always works out best, someone may not like the situation,...but it sure beats the hell out of being humiliated by finding out after the fact.