Not good enough for my bf's kids

Brandie • I am me n I love my boys!!!
My SO and I have been together 11mts and in that time he just started getting over night visits with his boys a few mts ago, which is great I am so happy for him as I have 2 boys of my own and now we are expected one together. My SO does everything for his boys, bathe them, cook for them, etc., well today my SO has been sick so I thought I would give them a bath and get them ready for bed for him. I am doing great til his youngest son starts crying when u go to get his hair wet and rinse it like he does when his dad (my SO) does it, my SO comes in the bathroom questioning what I used on his hair, I told him the baby shampoo what I am suppose, he gets pissed at me for I don't know what and tries pushing me out of the way, I tell just go goes I have it, I hate when my SO rinses his son's hair cause he gets mad at his son for crying, I just let him cry. I got 2 kids older then his I do believe I know what I am doing, maybe I am wrong or not good enough for his kids?! P.S. I let my SO help with my kids cook for them, get them up for school, etc., we ain't no better then him or his kids we are all equal or atleast that's how I feel or felt