Custody question...

Ok SO, my fiancé and I have been trying for months to work things out and i think it’s all finally coming to an end. My fiancé comes home from work and spends 20 minutes MAYBE all night with our son. Most of the time he goes places and never offers to take our son. He says it’s too much of a hassle to take him in and out of his car seat. So if he’s not on the couch sleeping, on his phone or watching tv, he’s hunting, fishing or taking someone’s on call. He also leaves a lot and comes back high. I dont think it’s fair if we get 50/50 custody... I’m the only one that does anything for our son! He’s never watched him alone. (He’s 18 months) I really don’t know how the whole court system works but I was wondering if you could give me and idea of what our custody arrangements would be like? How often will I see my son? It absolutely breaks my heart knowing that there will be a time I won’t see him. I love my sweet boy so much. I stay at home with him everyday except when I go to class(nursing school).

Also, Will his dad get over night stays? He’s never put him to bed since he was very little. He holds him down so he can’t move until he falls asleep and tells him to shut up when he keeps crying, it breaks my heart.

***I am in no way trying to keep my son away from his dad. I just want to feel like he’s in good hands when he’s away from me. If he hasn’t been a good role in his life for months now, how is it going to automatically change?