The author copped out. Okay, the axe came and he had to deal with it. One can say he kept the story open to keep it open for a continuation, but how would that turn out? "It's been already 4 months and I didn't give them an answer" "Now we hate you! (But we actually don't)" *drama*drama* Truth is he didn't want to disappoint half of the readers (as we do split in around 50:50 as I see it). Chicken!
And it's a bummer, because even if the right girl wouldn't have won (depends on your favorite), I believe most of the readers would have accepted it. Not every story allows that hard cut. It's a missed opportunity. Given, not every author can handle heartbreaks as well as in
Midori no hibi (Read it. It's good.), but it would have definitely made a better, more satisfying ending. (At least he didn't go for the timeskip skipout.)