Well I'm kinda on the fence if this should even be seen as cheating/NTR I mean the premise is that the MC who's been a virgin all his life goes on a few dates with a girl and they have sex and he instantly get's smitten (cause he lost his virginity to her pretty much) and wants them to start dating with marriage in mind, which is a pretty common way in JP to start a serious relationship of bf + gf. But then she tells him that well you suck in bed and sex is important to me and besides I'm already seeing multiple guys since my libido is so high.
To which he just goes oh but just gimmie a chance to improve my bed game, has no clue how to get better so he turns to the girls other sex friend and then from there the plot can pretty much evolve into the MC getting all into seeing his girl being banged by someone else or something else.
But I mean the premise is pretty much that the MC tells the girl he likes that he's okey with an open relationship from the start since before that point their not actually a couple and instead he tells the girl he's okey with her sleeping around so that they can become a couple but that he hopes to eventually become good enough in bed that she won't have to sleep around. He even goes as far as asking to watch them having sex so that he can get better at it.
Then later on the game evolves into 3 different endings spoilers ahead.
I would say this is more netorase then netorare since the MC from the get go asks the girl for an open relationship so they can become a couple, he then also asks to be told about her having sex with the other guy, asks the other guy for tips and also to watch the two having sex. He also seemingly likes watching the other guy bang the girl. Though as the player you can pick if the guy wants to step up and have sex with her on his own or if he likes watching more. It's also unclear if there is netorare even in the so called netorare route since the MC is still together with her and is seemingly into it...