HE LIKES OTHER GIRLS PICS😕

So I’ve been w my bf a year. I hate when he likes girls half naked photos on Instagram. It’d be fine if it was a normal pic but it’s of random girls in bikinis. Around a month or 2 ago I had a talk w him about it and told him I didn’t like him doing it. He said he would stop but has he? No. He continues to do it and to make matters worse he makes jokes about it. The other night we were on ft and he was like “guess what I’m doing”? And I was like “what”? And he said that hes liking a girls bikini pic and said “niceee” as he was doing it. It just rlly bothers me. What r ur thoughts and what should I do?