NTR is more about loss. in principle is a tragedy. sometimes comes from that sense of entitlement that people have towards others.
my dog is loyal to me.
my wife loves me
my mom coddles me.
my best friend is always behind me.
my country wants what is best for me.
when that entitlement gets taken away by circumstances is when you get a feeling of something being taken away while you were asleep.
my dog left my house because the neighbor kept giving it treats.
my wife was just pretending to be happy to hide her dissatisfaction, and i see it know that some one satisfies her.
my mom found a new guy and her attention is on him not on me, she wanted someone to coddle not to coddle me.
someone poisoned the relationship with my best friend.
my country decided that what was best for me was to rot in a cell.
NTR is as simple as
hey buddy lets meet up at the gas station at 6:00PM
sure man lets go!
you stand on the gas station and call him: what happened man its 7:00PM
Im sorry bud, X picked me up to his party I could not hear the phone sorry I missed the time.
then they make another day and the friends fails again. when you look for him you find him drugged at X's party. X tells you to fuck off as they are best friends now. and you loose a friend.
NTR without sex.
using your example
- MC and female have a deep relationship. MC has a crush and female always indulges him whenever he proposes an outing. they watch the stars/fireworks/ go to abandoned houses, play videogames whatever....
- another starts taking her away (through blackmail, plain romance, or a good dicking, or any other viable method)
- MC also finds himself in circumstances that keep him away from her. a trip, a mystery, a promise, a debt.
- she begins ignoring the outings. canceling plans, and making excuses. Basically altering her relationship with MC.
- MC finds out and reacts according to his personality.