Torn.. please help

Idk who to believe my mom or my boyfriend

My mom claims that she saw my boyfriend “mistreating” my son. She lies for no reason she told my Bestfriends Mom that I go to my SO Job trying to get him fired. She also denies the hell out of having a boyfriend that used to beat up on us as kids.. anyways She claims my SO Wouldnt let him play on the computer so my son started staring at him and then my SO stared back and then my son said “I don’t like when you look at me like that” so my mom told my son to come sit with her and then my son started crying my SO took him in a different room to talk.. and when she came in my son was crying harder and gagging but idk what to believe. My mom was implying that my SO was making my son cry somehow. I know my mom blows everything out of proportion regarding my son. And her story isn’t even concerning.. Anytime someone tells my son “no” he comes crying to me wanting me to help him have his way. Anyways my boyfriend and I are expecting a baby and since day one my mom has been Angry about it.

Today my son came upstairs to tell me that my SO Wouldn’t let him play on the computer so I told him that my SO Is on there and he needs to wait. My SO came up stairs to tell me that my mom was mad because he wouldn’t let my son play on the computer and she started babying him so my SO took him in the garage to talk to him in Private since she wouldn’t butt out. I go downstairs and my mom immediately starts telling me that I need to watch my son around my SO and I need a better relationship with my son because he feels Like he can’t talk to me. I told her that she doesn’t know what she’s talking about. My son tells me EVERYTHING. Anytime someone mistreated him or tells him no he comes to tell me. We had issues earlier in our relationship after it got serious because I wasn’t comfortable with my SO disciplining my son (taking toys away when he acts up) I felt like that was solely my job. I talked to my family and they all told me that if it’s someone I’m serious about then I should allow him to discipline or else my son as long as he’s not hurting my son. My mom even said today that she respects my SO and feels like he’s a good guy and wouldn’t hurt my son... so then why the big fuss?!?! Idk I plan on talking to my 5 year old when my SO leaves but I just wanted opinions. What would you do? Who would you believe ??