Omg you're so dramatic!! It's not like he CAN'T have normal sex, it's just that the omega was a VIRGIN before he did it with the seme in chapter 1, so it's normal that he is reclutant in having sex when he's not in heat (when omegas are in heat their bodies are naturally more "open", I don't know how to say it), but that doesn' t mean that they don't do it when they are in a normal condition!! At the end of the story the uke even started to enjoy normal sex, as I thought, it's just a matter of practice cause he never did it with anyone before Renjaku!
About the brother thing it's fucked up but omegaverse are essentially based on animal instincts so...
Like wtf the parents are now suddenly okay with their son after fucking abandoning him??
Also why is no one in the entire story has a problem with 1- brother lusting for his sibling for over 10 years and 2- trying to rape him TWICE?!!!
the plot development doesn't make any sense. And basically saying you can't have sex if you're not in heat means that all actual gay relationships are not valid since you need women parts to have sex.
This is one of the reasons most omegaverse stories suck (yeah there are some good ones out there like tidal waves). They authors just treat the ukes as males with female parts and if don't have the parts you can't have sex with a man. So in a way it's phobic.