Ermm.. in a bit of a predicament :/

Apologise to you neighbour. Clearly state that it was an accident, and that you wish to be friends and nothing more. It's not a big deal, as long as it means nothing more to either of you than a mistake.
If you feel like you would rather be with this neighbour than your boyfriend, break up with your boyfriend at once. You made a mistake, yes, but it was wrong. If you don't know who to be with, have nothing more than friends to do with either - you are not ready to be committed to one boy.
So you basically have three options - go with your heart.
Hope that helped a little!