The answer is that you cannot find out with any certainty unless you ask him the question, and unless he is willing to give you a truthful answer.
One possible clue, is to observe him when a man and a woman come into a room. Does he look at the man first?
or
if the guy has a tendency to look at the crutch area of another man
or
you can try asking the guy to perfom oral sex on female partner, most well all of the men will enjoy it … but … homosexual men will find the thought of it repulsive.
I would have thought most girls wouldn't be able to tell.. there might be little clues like he doesn't seem that interested but then again that could be anything.. depression, stress or if it's an arranged marriage the fact that he just might not be attracted to u in particular :( If it's a love marriage imo he's prob more likely to be bi (otherwise why bother.. a desi gay guy would prob wait around till the last possible moment unless he was being forced) Dunno if that's better or worse.. Also, he could have just been 'experimenting' (due to curiosity or drink or drugs).. Again, dunno if that's better or worse..