Is it offensive?

I'm pregnant and my boyfriends friends are placing bets on if the baby will be black. Me and my boyfriend are both white. I was so upset when I found out and asked him to immediately cut them out because I think it's disgusting that they would think I cheated. He just shrugs and says it's okay and if anything it's more offensive to him because then he would be the one that got cheated on. I don't understand how he can be so chill. Wouldn't you be upset too? 😡