Fukurou is definitely going to end up with Rei. Since Ootaka is already dating Suzume, and Suzume doesn't like Rei at all besides childhood friends. Also Rei's love towards Chun (Suzume) isn't that, er, "passionate??" I guess you can say... Seems more like a brocon, not really true love. So fret not! Rei will end up with Fukurou I assure you uvu
that's because the beginning of the story is where the main characters are introduced, so it would be weird for them to be like "look here's the main characters, but we're gonna hook this guy up with someone else and the other main is just left to be depressed :D"
But they could do it if they introduced all 3 guys at the beginning. or they could just do it, but like i said, that'd be weird
There's a story (bl) like that though...im not sure of the title: Shitsuren Mania
I still have yet to happen upon a yaoi or shounen-ai where the kind uke ends up with a different seme because the initial seme was either 1) unfaithful or 2) pushing the uke away for one reason or another (for ex. denying the fact he is in fact also interested in men and crosses the line, only to be too late in taking the uke back). Either way I look forward to the progress....maybe he'll end up with the friend? :>