cheating? feelings?

so long story short, back at the very beginning of my bf and i’s relationship, he cheated on me with a girl from his class. well fast forward to 3 years later and I was on his phone and saw he recently liked one of her pictures she posted back in MAY. obviously he did that to try to get her attention right??? what do y’all think? I’m scared to ask him about it because I feel like he’s gonna get mad