(Usually) men turned on by their wife, gf or crush being with someone else. May also have dub/noncon or other dark elements. !Warning! This is often a hidden plot twist so if you dont want spoilers, back out now unless you're searching for more of this goodness. For me, discovering one always feels like christmas!
This theme often goes with ntr/netorare (shocked to be betrayed but surprised to be turned on) or netorase (their kink).
Other NTR list:
https://www.mangago.me/home/mangalist/2130423 
Anata no Okusan Moraimasu