I think NTR is about heartbreak and loss whether you or the other guy feels it is the key point that connects them, Murder is Murder whether you are the one killing or being killed.I just checked a couple Japanese sources out of curiosity, and NTR only ever stands for netorare. One source did say that there were instances of it being used for netori, but it was basically just a footnote—other sources didn't even mention it. Nowhere did I see any mention of netorase.
I've seen a bunch interpreting Netorase as meaning "someone who is sexually turned on by their partner having sex with someone else", I never really agreed with this, I always interpreted it as someone who loves their partner so much that they give permission for them to have sex with another person when they are unable to satisfy them themselves (usually through injury or illness)
(example in Glassix (where you can convince an extremely ill man to let you fuck his wife (And eventually steal her from him)).
They are still experiencing the loss that is felt in netorare, though in their case they are jumping on the grenade, rather than being wounded by someone else, The partner always seems to leave them in the end, emotionally if not physically (which mirrors Netorare)
[And no I'm not claiming my interpretation is THE correct one, it's just what makes sense to me and what image is conjured when I see the word]