
At first, the seme really pisses me off for being so insecure and overthinking everything. However as I read the last chapter, I find myself forgiving him.
After all, There's no such thing as a prefect relationship. There is always their ups and downs and lets consider this the biggest thing they face in their relationship. Plus the ending is so sweet. How can I not be happy for them?

Why would someone piss you off for being insecure and overthinking things? That's not why he pissed me off, after all, either. KTBN.

I summarize it as being insecure but if I had to go in detail about how his action made me angry it's probably because his insecurity hurt two other people who truly love him. Sorry I was confusing.
I mean how would you feel if a guy dump you because he thinks that you're relationship was a mistake? I'll be mad... not because he was insecure but he never once try to talk to Yuuki about it and then he just dumps him using pitiful excuses and trying to find a different route with someone who he didn't even love to protect himself.
He even mention it on this page
http://www.mangago.zone/read-manga/life_senjou_no_bokura/uu/life_senjou_no_bokura-chapter-4/15/
that the main reason he dump Yuuki was because he was afraid that Yuuki would leave him one day so he decided to dump him before getting dump. I just felt so bad for Yuuki.
Which is probably the biggest reason why I was so mad. It's because I really like Yuuki as a character (so I'm just biased) and it was painful to see that poor boy suffer for so many years. Unable to move on or find a new happiness with someone else while Akira could at least find some (tiny.) comfort from his new life and family (even tho it didn't last)
By chapter 4, I felt bad for his wife but at least she eventually find someone who really loves her. I was really happy that he grew some backbone to tell his wife that she's not the one he love. However, I was still mad at Akira but I was overjoy to see that he deserve what he was getting by hurting two wonderful people but I was happier by the fact that he realize his mistake and went to find him because even if what Akira did hurt Yuuki a lot, they did made a one heck of a cute couple.
By the end of there series, seeing them both so happy, I can't help but be happy for them as well. Akira learns his mistake and love Yuuki as much as he could for the rest of his life and Yuuki seem really happy as well.

When witnessing a couple be that intimated in public. The girl with the angry look has the right reaction.
http://www.mangago.zone/read-manga/saku_no_kono_hana/mi/2e1bf7f15da47c08e5da6726e638877b_chapter-1/12/
You're gonna get arrested if you have sex in the middle of the streets (plus in front of so many people).... ヽ(`Д´)ノ

Reading halfway of chapter 1..... first thoughts.
Uke: I was invited to his house under the pretext of becoming getting along better.
At the house: Seme starts to come closer to the uke.
Me: dude..... a couple pages ago he said that he got an erection from seeing your nipple. Have some Self defense but what am I expecting? self defense is almost non existence in the world of yaoi.

Regardless of the excuses, the seme is cowardly and unworthy. Because he wanted a normal family? Because he was afraid that Yuuki might leave him first so he decided to break up with him and without a proper reason. He is just running away from his own insecurity.
If anything, I'm happy about the seme getting hurt in chapter 4. It's sad and heartbreaking but he deserves it! >:( How can he hurt such a wonderful guy? Hopefully he learns to treat Yuuki better otherwise I'll break his dick in half.
Thanks Yuki for being so wonderful. Tho you forgave him too easily in the end, I think he needs to beg more for your forgiveness.

A couple things I would like to mention
First off I really love Bart. There's so much flashbacks of him and from what I've seen, he's such a sweet and honest guy! He cares for his brothers and the people around him and to protect the castle. Such a fine gentleman and knight he was... Really hoping that he was reincarnated T_T But we all know what happen to him...
Second, I kinda ship Hiroki and Minami... Althrough Minami is dating Takao... Probably because I ship Veronica and Glen so I think that Hiroki and Minami have great chemistry....But then again, I thought they made a pretty good couple before we found out that Hiroki wasn't Bart.
As for Takao, I thought she was kinda cute at first but after she regain her memories from her previous life.... She became so uptight... like she doesn't question anything or say anything more then necessary, just blindly following Minami around. I literally don't see her as Takao anymore, instead all I see now is Rida... Which is probably why it doesn't feel like she is his girlfriend.
Nothing wrong with loving someone but someone who fuck someone else just because they sleep with the guy he likes is kinda mess up.
Then again they'll all kinda mess up in their own way