You're totally entitled to your opinion but from the way I see it, you completely missed the point of this manga. Sure, you noticed the ex suffering but did you notice how the uke suffered just as much, if not more? To be pining after someone for years and then be told that he was going to leave you for someone else (regardless of whether he loved the other person or not), you can do nothing but wish them the best (even if you're dying inside) because you don't want to be a burden to them.
From the way I interpret it, the uke was able to let go of his past feelings and find love in someone who loved him unconditionally.
Another thing is, I really don't get the point of the ex marrying some random girl when he was so ill that he couldn't do anything with the uke, maybe he did it to appease his parents? Whatever the reason, he was acting selfish when taking that decision, so yeah I do pity him but I don't feel bad that he got rejected by the uke afterwards.
Honestly, you're missing out on lovely story and you should definitely give it a chance!
I feel really bad for the uke's ex boyfriend, he didn't break up with him because he didn't want to be with him anymore. He broke up with the uke because he had a weak body even tho he really did love the uke and married a woman when he didn't want too and end up suffering, he went through hell and now he can't get his happiness with the one person he truly loved? This is why I hate these types of romance stories in manga where the main character's ex breaks up with them for some reason when they didn't want too and end up suffering, I stopped reading this Yaoi manga because I couldn't handle it. I am tired of seeing this bullshit in manga, the uke's ex boyfriend deserves to be loved way more than the seme. I'm not even happy that the uke found a new love, as much as the uke's ex boyfriend was suffering it made me sad that he couldn't get the one he loved back. I thought this was going to be about the uke having one sided feelings for someone a long time ago but nope, it made me actually care about his ex boyfriend more than the uke and the seme. I rather read a Yaoi spin off about him then finish reading this manga, I'm sorry that I'm being so toxic with this Yaoi manga but I just don't like it that the author went this way. I would prefer if he just had a one sided love, I've read worse Yaoi manga than this but I didn't like this and couldn't continue for that reason ╥﹏╥