Am I overreacting?

Kind of long sorry.. :( please comment for advice that you have for me. My fiancé works nights 6pm-2am. Sometimes doesn't get home until 3-4am. I let him sleep in until 1pm. During this time I'm taking care of my 1 and 2 year old step sons. On weekends he wakes up with us and so on. I'm 34 weeks pregnant with a sprained ankle right now. Once I wake up with the boys I change their diapers, new clothes, breakfast all of it. On weekends my fiancé doesn't even do that. He just sits around on his phone and doesn't even change his boys diaper and once I ask him or even tell him sometimes to change them, he throws a fit! His youngest wakes up with a full diaper of poop and it's everywhere even when I change him before bed. Well today I've been staying off my foot and once the youngest one wakes up, he brings him out to me and makes me change him and then walks out to smoke a cigarette. He never gets them out of the crib and then changed them right away!!! But I'm not going to leave him in a poopy diaper so of course I change him. I leave the oldest in his diaper that is just pee to even see if he would change him and of course HE DOESNT! Then today they went to a birthday and I couldn't go because my ankle and because even though I have a sprained ankle my fiancé would still be like "go chase him down, or change his diaper" so I just stayed home to get some rest and I told him this. Then he asks later on "so while we're gone can you do laundry?" LIKE NO!! You could of done laundry all day and I'm trying to stay off my foot! I know I will NOT take his bullshit when I have this baby and he's still pulling this shit! Am I overreacting or what?😤 edit; i feel like sometimes I care about his kids more then he does. I know I will not let him just do this to me when I have my baby.. Why am I "letting" him do it to me now.. I'm not really letting him because I do tell him that I feel like I'm being disrespected and I'm just not gonna take it! But I feel like I would leave him if he was doing this to me when I have my baby.. But I could never leave him now.. I couldn't imagine leaving those two boys😣