My boyfriend called me “slut”

I posted an old picture on Instagram with one of my best friends in a party, this picture was taken almost 3 years ago! And my boyfriend saw my post and got mad at me, he said that I was posting “slutty pictures” on Instagram so everyone could see me and that that’s what I liked. I couldn’t say anything to him because I was shocked and I was just like “did you just called me a slut?” And he only answered “okay” it was all through WhatsApp because he’s working rn we’re both 18 years old and we’ve been dating for 4 months. Please help I don’t know what to do!!