If there is something ridiculous about this manga, it will be the fact that there is a 10-year age gap between Rei and Jinnai. Come on, they look like friends around the same age. May be Jinnai just simply has a skin care secret chuckle
That aside, there is nothing else absolutely unrealistic about the relationship depicted in this manga in my opinion. Firstly, regarding why there are so many ukes who need to be taken care of in the yaoi world, the answer is quite simple. Most yaoi mangas are written by female mangaka and for target at female readers. With that being considered, many of the stereotypical characteristic of women are carried over to the ukes. I am not saying that all female are weak and undependable, but there are things that are expected more from the males. There are women who preferred to be treated exactly the same as their male counterparts, just as there are some strong image of ukes in yaoi. But over all, that explains why it is quite rare to find seme-like uke in yaoi and more in bara, which actually aims at male readers. Of course I personally am not a fan of cutesy girly ukes because they are guys after all, but Rei was not quite portrayed so here. In the end, he furthermore made a brave decision to break the family shelf, to stand for his belief; so it means that he has learnt and matured more though out the story and I don't see how Rei could be called an incapable person after all of that.
Secondly, regarding the complaints that Rei was so clueless, naive and that Jinnai was kind of forcing Rei into the relationship, I agree but only to some extends. Rei was indeed naive and clueless, but only in love. He was not a clueless as in thinking that life is pink and everyone will live happily ever after. In fact, due to his family situation, it is reasonable why he has not been able to go around dating and to have experience in sexual attraction. I have friends who have little or no clue about this matter too just because families are too strict and most of what they do are studying, working, or hanging out with friends while having a hard time to start a relationship. And as you can see from the manga, Rei struggled to become more socialize because he has not been exposed to the outside world a lot. It was not his fault to begin with while he indeed made effort to learn and improve. Therefore, just simply characterizing himas "naive" and "clueless" is a little unfair. Also, Jinnai did force Rei to consider their relationship. But it was Rei's consent that started their relationship as Rei claimed that he was very well aware of what they were doing and chose to let Jinnai do it. So Jinnai was not forcing Rei to do anything actually.
Last but not least, this yaoi is dramatic as it is categorized. There were issues keep coming, there were jealousy, but they were brought up in believable situations. Jinnai did not randomly become jealous because Rei talked to a friend and vice versa. Kimura did make some moves to threaten their relationship! Unless you are saying that you absolutely have no problem with your lover being around with your love rival, I don't see why anxiety is unacceptable here, and it should have nothing to do with trust or not. Also, insecurity over social gap is realistic problem. It might not happen to everyone, but it certainly happen to and trouble someone in real life. After all, this is a dramatic manga, so please do not look forward to finding a completely sweet and peaceful relationship but drama!
Disclaimer: I am not worshipping either this mangaka or this manga. I cannot say that this is the best manga of Hinako Takanaga sensei or by any mangaka either. This manga has to have some flaws but I would like to point out that I don't neccesarily agree with some pointed out by other reviewers. Also, this is my opinion, and I by no mean want to force it on anyone because I believe each of us has our own standards and philosophies.