Boyfriends son and crying

So I'm dating my ex friends baby daddy... Plz don't judge but how our friendship ended I feel I owe her nothing. They have an almost 6 year old together. Back when we were friends when their son was 4 my friends boyfriends (not the baby daddy) would call him a pussy for crying and say she needs to teach him to be a man since his dad isn't. So mean to him. She's still with that guy but my boyfriend and her have split custody. Today my boyfriend was stressed and started crying and his 6 year old put his hand in his face and said "Daddy?" And my boyfriend said "Daddy's crying" and put his hand on his son's hand and idk why but now I wanna cry🥺