Can step parents be confusing even as an adult?

So my mom got a new boyfriend and married him before me and my siblings met him, which is fine, we’re all adults so it’s not that important. Well I met him a few months ago and he’s great! But idk, he does act like a father to me and I’m ok with it, but it does make me feel a bit weird. All my mothers past boyfriends/husbands have been physically abusive towards her except my father and her last husband told my mom he was going to kill me and my siblings and it was the only time we ever felt we needed to load the gun in our house. That day was very scary and the police found him with a knife in the garage while we were in the house. Or I remember how my dad told me to run to an adult if I ever saw my moms ex boyfriend when I was kid. I didn’t understand why, but I knew I had to do it anyway. So it’s nice he’s not like that and I can tell he’s not faking anything, but it’s like I get anxious is he ever does seem to get irritated or annoyed by something. I get scared he’ll become violent or start yelling, which he never does and he’s in a good mood just seconds later. I hugged him for the first time just a week ago and it felt weird trusting one of her partners so much because I’ve hated ALL (not including my dad) of them. I’ve never trusted a single one or was able to feel comfortable around them. But it’s different with him and now it’s confusing?