Am I crushing or just over analysing?!?!

Hi. So for a while now me and my partner have been in a bit of a bumpy road of our relationship.

He hasn't really been giving me much attention unless we are in bed, he's being very selfish and aggravated.

He has a brother and me and his brother get on very well and when I'm up at his place I speak more to his brother than I do my own boyfriend. I feel like I'm gaining feelings for his brother but I dunno if it's just because of the attention I'm receiving from said brother.

I have no idea what to do.

Also this guy is my first boyfriend and I'm 20 years old. Any help would be amazing.