Let me explain, as title isn't that specific. I'm looking for shounen ai/yaoi manga, that focuses on developing relationship between main characters. As I was reading a lot of different titles, I realised I'm totally a sucker for stories where characters slowly get to know each other, become friends, later start feeling something more etc. Those are usually shounen ai titles, as yaoi tends to get to sexy stuff way faster, or even start with it, where I want slow, slice-of-life stuff. As for examples, those would be:

• Koimonogatari (this one made me realize how much I enjoy stories where characters slowly get closer, I almost wish it never gets to romance part, I enjoy their friendship so much, haha)
• Seven Days (even though it only takes 7 days in this one, it didn't feel rushed for me and I enjoyed the whole "getting to know each other" so much)
• Slow Starter, Blue Sky Complex (same author, so I'm putting them together)
• Blue Lust
• Saiyaku wa Boku wo Suki Sugiru
• Monster Petite Panic (short, but it was adorable, I wish it was longer and more developed)
• Hidamari ga Kikoeru (enjoyable, but I think I liked it more before romance plot. Most problems are because main characters just won't say something is wrong and I hate misunderstandings like this)

Also, I usually tend to dislike childhood friends plot, it doesn't allow that much development in a relationship. I like longer stories, but if it's good, I want to read shorter ones too. Can you recommend me some manga like this? 😀

I'm in the same boat as you. I've just written a topic about it here. As you explained, in most of the yaoi manga out there the relashionships seem to be based on sex more than anything else.

My recommendations are actually all manhua/manhwa because I've noticed that Korean and Chinese works tend to be more realistic and focus a lot more on developing the story and characters:
Guang Xiang is exactly what you are looking for! It talks about two young boys who gradually grow feelings for each other. I don't want to spoil anything but you should go read it right now. Believe me, it's totally worth it!
Hate Mate: I appreciated a lot of things about this one, especially the end. I think you should give it a try.
At the End of the Road: the main characters are two childhood friends and I don't know if it meets your requirements, but it was beatiful and I read it until 3am so... maybe you could add it to your wishlist for the future 😉
Roommates (Young Seok): it was a really nice reading (and my second gay-themed manga ever, so I'm attached to it). Keep in mind that this one is a light reading and it's filled with comedy too.
Never Understand: I still re-read some parts once in a while. I think it meets your requirements.

Well, these are my recommendations. I know you asked for manga and I answered with a list of manhwa/manhua, but I can't find Japanese manga that meet our expectations so...
Guang Xiang is the one I recommend the most, but the other ones are also very good! I hope you will find something that suits your tastes in this list 🙂

Thank you so much for recommendations! I said manga, but I definitely don't have anything against manhua/manhwa, it's simply that I've only read 20 of them at most, haha. But it's actually good, because I don't know any of the titles you recommended and all of them look promising, definitely starting Guang Xiang right away 😀

And really, there are so many stories where love starts with sex, or characters end up together in first chapter just because author wants them to go to bed already, it's almost hilarious, as there is no relationship building at all. To be honest I don't even mind the whole "I'm generally straight, but you're special", or if story just doesn't really mention orientation, because things like that could happen, but I want it after believeable relationship building, where you can understand why character thinks "We're so good together, so gender doesn't matter" haha. I somehow just love this whole slice-of-life everyday where you can see characters get closer to each other, I enjoy the development more than result 😀

I'm glad I could help you!

BTW, let me know if you like Guang Xiang or not. Even if you end up not liking it, I'd like to hear your opinion. If not here, through a PM. Well, only if you want, of course 😉

Oh gosh, I just posted a thread like this I feel so dumb.

Anyway, I can't recommend Hana wa Saku ka enough, it's absolutely gorgeous (or anything by Shoko Hidaka). Given and Kikoeru? are quite wonderful as well. And if you liked Seven Days, you have to read Hana no Mizo Shiru by the same artist.

Thank you so much for recommendations! I've read Hana no Mizo Shiru, but I didn't read the rest 😀 since you're also looking for stories like this, I can recommend most stuff from my first post, haha.

Yume no Kodomo
Complex
A Man Like You
Yume Musubi Koi Musubi
Himegoto Asobi
Oko-sama Star
Merry Checker
Harete Bokutachi wa
Michiru Heya
Yellow
Window to Window
Zetsuai
Sakura-Gari
Doukyuusei (NAKAMURA Asumiko) You probably heard about this one because of the movie which was released, but I still thought of mentioning it.

These are mangas i feel had some development 🙂 instead of the typical "let's fuck" The end.