ouch! thats really got to hurt.well, first of all dont blame urself, u werent to know.
u dont really know if they'll last it out either! so i guess u can always hope...a little devious, but hey, as youve just seen its a selfish world!
2ndly, you dont really know if these people were spendind lots more time together than u 2 were, not forgetting their on the same corridor, and maybe, he just got to know her a lot quicker and decided to go out with her, not giving you a chance.also, he may have been unsure if you liked him in that sort of way, and perhaps just thought that you saw him only as a friend, possibly explaining the reason you still really get on. but, theres hope, perhaps he likes you, but was confused by whether you felt the same or not.
dont worry, takecare
lots of love
xxx