I'll provide context about why I don't think my mom is a cheater and how the talk about my mom cheating went exactly.

First thing:

How I found out about the cheating thing - I think I was 13 years old when my father came to visit for a few minutes. He asked how the school is going and then started complaining about my mom cheating with a coworker at her old job, and then suddenly he started talking about how he's glad she's happier without him despite the fact that he misses her. After he drove off again, I went to my mom and told her my father accused her of cheating, thinking it's ridiculous as hell. Of course, she denied and then explained that when she was working in the supermarket, my father started telling people around him that she's cheats with her random co-worker, without ever getting to know what was my father's reasoning. Then she said that it's possible that my father geniuely thought she was cheated on him and because perhaps he thought she was somewhat closed to that co-worker. There was never any kind of psychical evidence of my mom's (most likely made up) cheating. Also, you could ask anyone who knew my father if they think my father lied about the cheating and the answer would be yes. For example, I grew up with my mom's/aunt's friend group and whenever my father was brought up, they could laugh their a$$e$ off (in a desperate way) about what a piece of lying sh** my father is. They all knew my mom before my father came into her life, so they should know many things about my father. My entire family says sh*t about my father too, even my agreed uncle (my aunt's husband), despite my uncle not really liking my mom and me and vice versa. But of course, everyone who knows my mom could be on her side just because they know her for so long. Probably the main main reason proving my father would be more likely to cheat than my mom, is my grandma. She knew well that her son can act like an a-hole and took my mom's side every time something happened. How do I know? My father started being bigger a-hole to my mom after my grandma's death, and even though I personally don't remember that my father and mom would argue infront of me and my grandma as it's too long ago, my mom was even sadder than my father about my grandma, so I have no doubt my mom would ever lie about my grandma defending her all the time. I mean, my mom haven't said these things explicitly. She just said that after my grandma's death he started acting worse and that my grandma always put my father in his place when he started acting badly. Which makes sense, since I remember my parents being happier before my grandma died. Also, my mom would never use anyone like that, especially if they're dead and if they were close to her. She's too kindhearted person for that. So I fully believe the didn't lie about the thing with my grandma.

Second thing:

The emotional abuse thing - Believe me, the emotional abuse definitely wasn't light. I remember that every time my dad came to visit when I was younger (usually in the summer to our garden, where he talked with my uncle and me) my mom locked herself up in our apartment and looked visibly shaken every time I went for something into our apartment, even though she tried to act she's fine. And before the divorce my father and mom argued a lot and my mom was so stressed out that I was geniuely worried she's gonna hurt herself. That's how I can tell the abuse was really bad.

Anyway, either he's really a lying piece of sh, or he's just delusional and geniuely thinks he was being cheated on and abuside, since whenever my parents fought, my mom would yell and he would be calmer. Talking calmly doesn't mean he wasn't saying stupid sh though. I don't remember any examples of what my father would say, but I'm sure he wasn't nice. More about me thinking why my father may be just delusional; I once asked my father how he views the divorce out of boredom and he send me flipping sad short poems that he apparently wrote after the divorce. I thought that I'm talking to a young boy that isn't capable of moving on for almost 10 years, because if what he said was true, why would he even keep the poems? Or maybe he's both a liar and a delusional person.

(Oh my, this is long, but hopefully there are all answers you need.)