Boundaries with “step-dad”?

My mother is engaged to marry her fiancé who will be my stepfather. They have been together for 5 years. I had my son a little over a year ago and when I did, I agreed that it would be okay for my son to call this man his “pawpaw” as my father is absent from our lives. Since my son was born, this man has been baby crazy. I’m so glad he loves my son as he does but frequently I feel like he has crossed boundaries. After I had my son he would come over and never say a word to me just take my son and babble away talking about how he was “pawpaw”. My mother knew how this made me feel and never said a word. She has always put him first above her own children (though we are all grown) even though he doesn’t put her before his child. I feel as if his behavior is only getting worse. Recently there was an issue of safety and he confided in my husband that he didn’t want to tell me what happened because he didn’t want me to worry. He has said before that “he knows what he is doing” as he has raised a child. I hate feeling frustrated with this behavior and I guess I’m just wondering how I could address this without hurting any feelings as I am grateful he loves my son so much. I just feel like there should be boundaries because we are the parents and he is marrying my mother.