feeding my baby oatmeal

I'm pissed my SO gave our 3 month baby oatmeal already without me knowing ! I go to babies r us with him to show him the baby blender I've been looking into because I've been doing research on what foods to start him on get him ready for solids . He says oh I already gave him some food .... damnnnnn couldn't let me know His family never inform me or just go against everything I want ! I don't want him sleeping on tummy they all do it now . I say no tylenol they buy tylenol ! Maybe I'm just mommy my feeling is hurt I literally broke down and cussed him out. Was I wrong ?