I can't say much about Towa's "sleeping around without feelings" because there were a lot ...

I can't say much about Towa's "sleeping around without feelings" because there were a lot of manga characters like that, and while it can be rather disheartening, especially if one of them already likes the other, it was just something that happens. It's especially a potential case if you feel like your feelings won't or aren't returned, or that you have a ton of insecurities. I see it in a lot of BL, so I saw it as "just something that happens sometimes, it is not the main part of the story, just a side addition that may contribute to it."

What I did feel unsettled with was how easy it was for him to just decide on sleeping with someone else. It gave me the impression that anyone would be fine with him, and it's not something to think about deeply. Never mind what's going on, never mind the circumstances, never even mind the thought that his buddy was with a girlfriend.

And then I came to think, he must be emotionally fragile. He only has so few pillars of support; growing up his parents were rather neglectful, and he's having trouble with his school life, understanding himself.
Soon, his grandfather, one of his most precious people, dies - and the only one who he could properly be with was Youji. Youji, who served to comfort him - not through a conventional way, nor did they properly love each other, but somehow, it did give him support. That's why he didn't see anything wrong with sleeping with other people casually, without feelings.

But then the bonsai-loving clumsy Kotaro comes along, and not only does he fall in love with him, he also meets with different view points and experiences, like his world suddenly expanded from being a stuffy attic to a warehouse. This man is clumsy, rather silly, but he is straightforward and honest. More than simply seeking comfort, more than simply going by idly in his life, not coveting more, his worries were slowly blown away, as Kotaro constantly shows his love and support for Towa, as well as the desire to be with him for a long time. Towa understands that beyond just seeing Kotaro as his type, as his friend, or as a person he likes,
Kotaro is a very important person.

After 3 years, it is shown that for once, Towa is being more honest about his feelings and desires, so that means he has finally found not just a pillar of support, but an oasis, a sanctuary, a home in Kotaro.

So, I soon grew assured. He has someone important to him now. Finally, he has someone who loves him back, and treasures him. His restlessness and worries won't completely disappear, but he won't have to deal with it alone anymore - he now has someone who is by his side.