Hello there boys, I need your advice.

Background:
- I'm 30 years old.
I was a pathetic nice guy until I was 25 years old, situations with women changed me.
- I've been with my girl for 8 years now, with a 1 year pause in between.
- We have a son, 4 years old.
- We live together, in her house.
- Almost every week I leave on Mondays and sometimes Tuesdays too, to visit my father and I sleep in his house (I still got a room there, just in case). This puts strain off of our relationship.
- Quarantine has me stuck here now, she's going to work because she's an essential worker, I'm working from home and taking care of our son.

Situation:
For one whole month my girl had trouble with a male coworker of hers, who is a basically a spoiled 24 year old child. They got along well but they started to clash to the point he wouldn't talk to her anymore, they're just 4 people in that office.
She told me he's always after girls all day long and I was almost sure he'd like some of my girl too.

She whined the whole damned month about trouble with this guy, every day she would come home to tell me what a fuck up this guy is and how the environment at work was tense, etc.

I listened, tried to give some advice the first times, then just listened because what's the point.
Suddenly, the problems were fixed. She told me one day she was going out with her coworkers, he was also going. I asked about the situation, she said all things were cool with him now, they talked it over.

I then asked what was his problem then, and what did he say.
She said she didn't remember and left it at that. She can be very forgetful, but I didn't believe her.
I fucked up, I should have faced her right then and there.

----

Fast forward a whole month, she comes home, says she had a good day at work, laughing and all.
I tell her it's weird how they are all getting along now with this guy (I hadn't brought it up again since then), she tells me she just speaks minimally with him.

So I tell her she never told me what he said, what his problem was.
She tells me she doesn't remember. I know her, she's lying, I tell her I don't believe her.
She tells me not to bust her balls. I looked her straight in the eye for some seconds, told her she's lying again. "I'm not lying, I don't remember, okay?"
K then. She's hiding something.

I retreated to my work and my interests, spent time with my son, absolutely ignored her from then on.
I think the problem here is evident, if this was the way around she'd be going crazy right now.
I won't assume anything but this is probably him telling her he wants a piece of ass and she doesn't want me to know, or she fucking up somehow.
This shit was last night, she went to bed early and has been basically silent, this morning included.

I'm not sure how to proceed, should I face her again, tell her to cut the shit?
Should I ignore her and keep on with my interests and work and son until she tries to come back?

I want to avoid this from snowballing if possible, all was good until yesterday.
A big fight with her could have serious consequences for me as I'd be the one leaving and that would basically fuck up my whole life, but if she's not willing to tell me the truth, that might be the resolution.

Any advice?
Thank you for reading.