Who should i believe?

so my best friend is in spanish with my boyfriend and she told him that i wasn't talking to him (just to see what he would say) and she said he said i don't care and then when i asked him about it he said he said why not i don't care and then i told her what he said and she was like what? he definitely said i don't care and then was perfectly fine the rest of the period, i wanna trust him and i've been best friends with this girl for more than 5 years (so i can definitely trust her, she tells me everything) and i've been wit my bf for awhile and i feel like i can trust him but he's been acting different later (he says it's only because of midterm testing and he'll change back to normal after) but i don't know who to believe and if i bring it up again with my boyfrend he might get mad and i don't want to fight. please help and please no mean comments. thank you