Ok so what i saw here is gen's dad makes reiji's mom fuck him cause he ran his real dad out of town? That's messed up so since they aren't in a relationship either he pretty much just uses her like a sex toy then and I'm still wondering if gen is gay for him he is right that's why at the end he said this is fine?
As easy as it would be to say up and leave I kinda get it, it's one giant circle of misery caused by lack of misinformation. It'd be easy to say they all need to talk it out, but a lot of these problems are historical.
A lot of this reminds me of 100 years of Solitude for some reason, one day a large enough storm will sweep it all away.
Basically this chapter de facto confirms that the author is his dad given we've not only seen his mother recognize him, we know this is his childhood home until he got chased out of town, etc. Probably explains why he almost committed suicide, too.
You definitely also get the impression here that Gen is trying to protect Reiji, and trying to justify to himself his deeds. If you remember, he doesn't like cigarettes, but he remembers when he was going to show Reiji the dragonflies mating and his father killed them with a cigarette. (Symbolizing a death pack of lovers) He clearly loves Reiji and wants to keep him in the town and at his side at all times, but he can never really be with him because he has a reputation being in his father's shadow, and he views it as his duty to continue his legacy. (I think the cigarettes are a memento of his father in some esoteric way.) The last lines are basically him reassuring himself of this arrangement, of his father using his love's mother as a prostitute, and that he will keep Reiji in this town where he can always be with him, even if he has to tie him down through a marriage and can't actually be with him.