A man is a cuck if he stays with a partner: and he finds out that the partner is unfaithful, and has remained unfaithful, or has been caught cheating many times. Cheating online, and also cheating physically.
He realizes others know of this infidelity, yet still remains with the partner. Everyone sees
the man as
ignorant, and as a cuck. The partners friends all know that
the man is inadequate and that she has cheated on the man.
The partner cheats with people that know the man is in a relationship with this partner. The partner and everyone she cheats with, views the man as a cuck. A pushover, who does not have what it takes to satisfy his partner both sexually physically, or through sexual talk.
The man has given up all self respect, and has decided to remain with the partner.
Sometimes the man
may do this because there are kids involved, and he wants to keep the
family together. So he tolerates her behavior and has no expectation she
will be faithful.