Netorare - SO gets stolen from the MC. Often by drugs, or non-consensual means. Or, if the author is completely unoriginal, MC has a small dick and along comes a big dick black guy.
Netorase - SO is shared with other people with permission from MC.
Netori - Netorare in reverse, with MC stealing some else's SO. Often very cringe.
Cuckold - Very close to Netorase, but comes with the connotation of the MC watching.
Corruption - Moral degradation
Cheating - Having sex with someone in a pre-existing relationship. (This one is more of a blanket tag thing)
Swinging - Like Netorase, but is mostly used in an "open relationship" context. IE, both in a relationship might be banging other people. (Also used for Netorase scenario's here, as the site lacks the tag.)