
1. Shouji (yakuza guy) is the father. Don't get confused. Touma said Ririko asked about Sentarou's address because she wanted Sentarou to take responsibility as the father. Because out of the 3 guys she slept with, Sentarou is the most reliable.
2. The fact that Shouji is not included in her will is very telling, since Ririko slept with him around the time she slept with our two mcs. It's probably due to the fact that he's involved with the Yakuza (dangerous) and he rejected her.
3. Both Touma and Sentarou said they used condom. Shouji said Ririko always tell him "I love you, I love you" even though he rejected her many times. We can deduce that she may have unprotected sex with the guy she loves (out of passion) unlike with the two mcs.
Review:
The art is beautiful but the story is lacking in substance and depth. It's sad because Touma and Sentarou have a lot of potential as characters. I would have wanted to see Sentarou publish music under his real name, even though it won't be super popular like Papaya, just to reclaim his sense of identity. Their love story is lacking build up and depth too.
Of course, we can all agree, that not doing DNA test is absurd. I thought it's going to be full-on comedy so I kind of let that slide at first, but it didn't.
I've read some of the mangakas works and I think this mangaka is plenty talented but needs a lot of improvement in their writing.

I'd like some more development on their carriers and the Sentarous relationship with the musician friend, like how did things end like that? I got curious. And what is Touma going to do for life now and a lil more of their interactions, until they admit they're family and Megu's development. Even so it was really cute but lacked depth maybe?

Yes, that too. His friend seems to have manipulated him. But, again, we're not sure since we didn't get the backstory. We were denied of Touma's character arc of getting an honest job and learning how to commit and be responsible in a relationship (romantic with Sentarou and as a parental figure with Megu). A lot of underutilized story potential.

People are upset that Fujita slept with his superior because Fujita (uke) even hated the idea that Kawasaki (seme) might have slept with Honda. So it's kind of hypocritical. At the same time, Fujita was the one who ended their relationship/situationship in high school saying that he's going to get a girlfriend. So it is quite valid to get frustrated with him.
Having said that, it seems that he was forced to sleep with his former superior because he said he can't quit his job.
Honda said Kawasaki didn't have any relationships but I see some comments here speculating that he could have slept with someone. No, he didn't. That was the implication. And that is why Fujita felt guilty and confessed he slept with his superior. To which Kawasaki replied, "I'm telling you it's fine".
All is well now. But it's disappointing how the mangaka added the sleeping with his boss part. It was really unnecessary to the plot. Especially, when Fujita seems coerced to do it too.
This is separate to the plot since Fujita was forced to do it, but sleeping with someone when you love another is not good. You'll just add one other person who gets hurt. I'm glad someone commented here that they've experience being the rebound person and how it was painful.
When you claim to love one person but sleep with another, it raises questions about the depth of that love. Perhaps that's an idealistic belief, but love is, by nature, idealistic.

i was disappointed by that part too, like it just felt a bit bitter..(just my opinion) but the storyline would have been fine without the forced sleeping part with the senior at work (like if it was just him making his moves on fujita and they were in the argument becuz of that)..maybe it's just me though...

This should have a higher rating.The way the mangaka writes the MC's (Shimizu) thoughts as a gay man is quite realistic, especially the part where he pretends to enjoy life by sleeping around while simultaneously loathing himself and longing for real love and commitment.
"Carry on fucking random guys and die alone"
-Shimizu thinks this to himself
It's very good, although the ending feels a bit rushed. We need to see more of the ML's (Okino) perspective. The fact it's not marked as completed gives me hope that there are extra chapters.
I would've passed over this based on the summary. It needs to a more appealing one that captures its essence. Also, we need more middle-aged BL like this.

"Hey, are we gay?"
"Well, that'd be how society views us?"
-I like this conversation because these days, I think people are too fixated on putting others into sexual categories. I've read comments in other BL mangas where readers express frustration when characters say "l'm not gay. I don't like other guys I only like you". But that does happen irl. As an asexual, discovering that there's a term for what I am is validating, but I don't want to be boxed in it.
Technically, they would be categorized as gay or bi but, ideally, there shouldn't even be categories when it comes to love. I believe people should just love one another for their heart and soul. But then again, we don't live in an ideal world so romantic and sexual labels are helpful in setting expectations and preventing future heartbreak.
-Everything is amazing until the SA part, which kinds of ruin the story and the mc's characterization. However, this manga is still worth reading for its realistic aspects, especially the homesickness and isolation in a foreign country, the racism, the doubts they have in their relationship (since they are both originally straight and very lonely in a faraway land where they can't speak much of the language). It could have been perfect but why write that part sensei? T_T
-One comment said that the art is fluid and I think that may be the best way to describe it. It has its own beauty and I read before that top art schools look for fluid or expressive art. I'm not sure if it's true though.

I'm rereading this today. Like @yoongibby, I also think that his name is Haru (spring) because when he said "It's not Mei. My name is..." the next panel showed cherry blossoms (sakura) but Sakura is usually a female name.
Also, in the following pages, it seems some time has passed, and Mei is now looking for a new job. In, mangas, we usually see artists use blooming cherry blossoms to represent spring while they narrate how time has passed and a new season and life has begun. It's a clever choice to keep his real name a secret from us readers. Only Dacchan, his lover and most trusted person, knows his true name and identity.
I wish Mei's trauma and the reason behind his promiscuity and selling himself were discussed more, but I understand that the chapters are limited. If it were longer, I would like the two MCs to have more backstory and development. On the other hand, I guess this style suits the story that has the word "Secret" in its title. As readers, are we are not meant to know more.

i really love this read! it makes me not want to know his name, I was peaking in at their love story but I'll leave them to it with a warm feeling in my heart
I agree! and thank you for leaving this comment! this wasn't written as a love story for a reader to place themselves in, we were allowed to see it but we shan't intrude, it's sweet ~
I like Godo more actually. I'm more interested to see him, who hated the serpent race, fall in love with Yahyul's cute brother. Maybe it's because I favor firey characters over less emotional ones. That's probably why it's a little difficult to connect with Yahyul. I feel that he's lacking something. Still, it's a good story and I'm glad they have a happy ending. It's finished in 61 chapters at battwo and I hope there will be extras.