Need opinions

So in 2012 me and my husband separated for about 3 months.. in the mean time he had a gf. Well my sil just had a baby and I commented on the picture and 2 seconds later I got a notification that my husbands "ex gf" commented on it to. And the girl and sil called each other by nicknames and my sil blatantly ignored my comment.. my feelings are really hurt.. am I overreacting?