YOU'RE the one who's calling "he hears his mom and her BF having sex in the next room" "abuse".
When I tried to explain to you that it's perfectly NORMAL for kids to hear their parents engaged in sexual activity...then YOU swing FURTHER to the extreme and say that any parent that allows their children to overhear them sex could be a symptom of other selfish behaviors that are destructive along with possible self control issues that could effect the safety and well being of the kids. and from that you swing even FURTHER and now we've gone from a kid overhearing his Mom in the next room to "exposed to illicit sex acts"!
I realize that you have personal issues regarding this matter and I sympathize...but YOU also have to realize that you're clearly allowing those issues to color your view as so noted.
The first time I overheard my parents having sex...I was embarassed. My Gawd...they were "OLD"..."old" people didn't have "sex"...ewwwwwwwwww. Once I got over my embarassment...cool, the old farts still got it on. Not long after...I spent the night at my GRANDPARENTS house and this time I recognized what the creaky bed springs meant and this time I thought: "go grandpa and grandma!"
I CAN see however, how a child could be frightened by the sounds...the "moans" and "groans"...the heavy breathing...etc; or walking in on their parents and thinking that Mommy or Daddy is being hurt. You do NOT "hide" it though...you do NOT "punish" the child...you do NOT treat "sex" like it's some evil, nasty thing...depending on the age of the child, you explain it to them in the simplist terms possible and you reassure them.