Pregnant by my ex and his new gf said..

She posted on Instagram “Can’t wait for my stepdaughter to be born!” as the caption to a picture of my ultrasound. They’ve been dating for three weeks (officially) but he cheated on me with her. I feel so down about it. I don’t know if it’s wrong for me to find this offensive or not. I don’t want to make my child be in some tug of war so I try to be quiet about things like this, but it really bothered me.