From what I know, the cuckold fetish doesn't include the loved person being stolen away, they stay with you.To clarify:
Netorare/netorase are both cuckold.
NTR = netorare, NTS = netorase
Netorare focuses on the cuckold’s feelings and often incites rage, jealousy (seething kind), anger. The Cuckold is often UPSET at having their lover stolen, though this can turn to enjoyment as they… accepts their situation.
Netorase focuses on bull’s feelings and does incite jealousy (but more casual, less dramatic). A significant theme is taboo and forbidden pleasure. The cuckold is WILLINGLY lending his parter out, as they find enjoyment in the taboo act. You know how incest is forbidden yet often fetishized?
Both cases can involve the lover being stolen, and their feelings also contribute to whether the piece is NTR or NTS. Sometimes the line is quite fine, and one genre blurs into the other. The cuckold can hate it at first then learns to love it, a pretty common theme.
You CAN have netorare with happy endings btw. It’s just rare and needs decent writing otherwise the NTR falls flat.
And it is quite hard for me to imagine how there could be a happy ending if the loved one gets stolen.
Edit: A caged cuck won't fuck his wife but she remains his wife.