Just remembered a manga I started reading a while back and ditched because it was unfinished.

It was about a girl who loves a guy and they go out for a long time and she is happy. But then suddenly his personality turns foul and he confesses he never liked her in the first place.

Another guy therefore takes the opportunity to be nice to the girl and the evil guy thinks he doesn't care but it is obvious he sort of does as he likes how she still loves him even after everything he did.
I have no idea about anymore because it's been a while.

The title might have had something to do with a pig or maybe the word 'baka' in it...?

Obaka-chan, Koigatariki ... maybe

Hmm from the title that sounds like it yeah thanks
I'll read it later and check but I think it is most likely that one.