<human>: Could you distill the essence of the text into 1-3 sentences?

Yup. You read that correctly. 21 here. 

Went over to my mom's yesterday morning. She convinced me to stay until Sunday morning. I don't want to listen to the guilt trips, so I stayed. 
Now, my mom had a friend over late evening. My brother and I dislike this friend of hers so we just lock ourselves in our respective rooms. Headphones on, Netflix and Spotify streaming. Same for my brother but replace Netflix with CS: GO and telling 12 year olds he f*cked their mom. My mom knows this and that she 99.9% won't see us for the evening. 

Here is where I went wrong: I was still up around 2 a.m. watching Sons of Anarchy. I decided to go get a refill on my drink.
Now, to give some context: my father passed away a few years ago. My mother has only had maybe one serious boyfriend that we know of since then. And has taken various trips, on her own, supposedly. Let's continue. 
 
After making it down the stairs, I take a few more steps and end up in the kitchen. Had I taken a few more steps, I'd have ended up in the living room. However, it's all open-plan so the kitchen is facing part of the living room. I see my 43 year old mother going down on her friend. I mean, really going to town guys. Nope'd the hell out of there with an awkward seal expression on my face. 
I don't think either of them saw me because of my position, the lighting and...their position, so I guess it makes it easier that she doesn't know that I know. But I know...and I saw. She was wondering why I'd left so quickly this morning.
<bot>: walked in on my 43 year old mother going to town on a slightly younger than her female, nope'd out of there and left early this morning.