Netorare means to have your loved one stolen from you.
Netorase means the same except you are the one who wants someone to have sex with loved one and most of the times you plan it. So basically the exact and proper equivalent to "cuckold". Examples are Netoraserare and orcsoft's game Kanojo wa Dare to Demo Sex suru.
In NTR2 the guy in the ends is so broken he is fine with other people fucking his loved one and even his daughter.