I’m sorry but wtf

Needed to vent. Idk if I’m over exaggerating or what!!!! But my son is a month old and he is breastfed and formula fed. Throughout the night I breastfeed because it’s more convenient than getting up making a bottle. Anyway! His dad and I aren’t together and my son went and spent the night with his dad. His dads girlfriend had a baby 1 year ago and also breastfeeds so she still has milk. First off, me and this woman do not get along so let’s start there. And I also want to say I never gave her permission to breastfeed my child. I send him with my pumped milk and his formula. I found out she’s breastfeeding my son and not feeding him the milk I pumped! I snapped off and my sons dad has the nerve to say, well I gave her permission to breastfeed him because he was doing that thing where babies look for a nipple while lying on her chest. Um what??? Excuse me??? I said Um yeah, he does that to me as well but he will take a bottle! It’s never a time where he just refuses a bottle at all. I’m livid wtf. Am I over reacting?!!!