Maybe there are already topics about this kind of thing, but since I don't really know how to search for them, I'm going to ask it.
Are there manga's about a gay guy and his life? I'm not looking for yaoi, that's why I'm writing it here. What I mean is, that the manga should concentrate on the life of the gay guy, and not on his sex life. Like, family issues, coming out, friends, dealing with homophobia, or other things like that. I've been wondering for a long time if there is anything like that. It would be best if the gay guy was the main character, of course. So if you know anything, please let me know 😉

Obsessed Yaoi Fan for 7 years ;D Way to go, me!

Welcome to Room #305! ? - It's about a homophobic guy who ends up roomming with a gay guy. I've only read a couple of chapters of this 'cause I thought the gay guy was really weird (and not 'cause he was gay). Quirky's just not my thing.

Oh, and there's a tag LGBT Character in a Non-BL/GL Manga, though it looks most mangas have that as a side character rather than a protagonist.

Yeah Welcome to room #305 is an absolutely lovely webcomic.

Hm... you could try doing a search for shounen-ai + slice-of-life too, since as mentioned most things in the LGBT character in a non-BL/GL manga category have those characters only as a side character.

Some suggestions...

Mainichi Seiten! has some of this, I think, though the first story itself is nothing special, the stories get progressively sweeter as you go on, so you should give it a try if you haven't already.

Otona no Mondai actually has the son of a gay man as the main character, but it deals a lot with what you're looking for, I think. It's also just a great, funny manga in general.

You could also try Golden Days where one of the major side characters is gay. It deals a lot more with broad life problems though, not just problems exclusive to those in the LGBTQ+ community.

And, yeah, definitely seconding/thirding Welcome to Room #305! It's definitely the closest thing to what you're looking for that I can think of. It also doesn't just deal with the problems of Hom, the gay roommate, but also deals with the problems of Yoona (a closet lesbian), and some trans* issues as well.

Sadly the genres dedicated to gay men (i.e. yaoi and shounen-ai) have very few manga deal with gay issues like coming out and homophobia in a realistic manner. But there are a few. Although some of these are yaoi, none of them are explicit, or focus only on sex. Here's what I remember for the moment:

New York New York

Nemureru Mori no Binan

Complex

Rules

Haven't read this yet, but Kinou Nani Tabeta? might fit what you're looking for

Maybe Koi no Kokoro ni Kuroi Hane? "A series of one-shots with a focus on how people around the protagonists deal with knowing someone who's homosexual, rather than the gay relationship itself."

Yaoi, but more about how they deal with it in the family: The Komukai Household's Circumstances

One of my favorite one is Shimanami Tasogare. It's honestly so heartbreaking at some points and the struggles that the mc had to go through was like so sad at some times. The start of the story is that the mc's friend found out that the mc was watching gay porn, he denies it saying that it was his brother playing a prank on him. And stuff happens, he wanted to commit suicide but then saw someone "jump off a cliff" then he went to inspect it, but then he found a lounge filled with some people who deals the same problem as him. And the rest well, you'll have to read the manga yourself

You should try Otouto no Otto It's about a dead Japanese guy's Canadian husband who comes to Japan to get to know the dead guy's family (his brother and niece). Unfortunately it's on hiatus at the moment, but it's a very realistic and at the same time empathetic story.

Shimanami Tasogare IS the #1 choice. It is I think the first manga that explicitly deals with LGBT as a community. I have read so many yaoi and yuri that deal with homophobia and all, but this one actually has so many different characters. There are even asexual characters! There is a focus on lesbians and trans people.
It is also very poetic.
I thought the ending was super rushed, leaving so many loose threads and more questions unanswered. For that reason I hope we can get a sequel or smth..

Welcome To Room #305 is also another perfect choice. Honestly, it has so much growth. It is quirky, but it is also realistic. Once you accept different sexualities, you start to notice that LGBT people aren't as rare as you thought they were. This is what happened when I came out. I feel like this is the most relatable story for me. I didn't exactly suffer from discrimination since I am surrounded by people who are openly pro-LGBT rights, but I do know some homophobes who changed their views after gettig used to me or to other LGBT people (btw it is a webtoon not a manga).

Other manga that truly deals with the struggle of a gay guy is a manga called Koimonogatari. There is also Smells Like Teen Spirit (it is a yaoi though.)

I feel like everybody has different experiences. I honestly relate a little to every one if them as a bi person, but I do think you should check the first and second one.

I've been looking for that kind of manga for a long long time too, but in the end I could find none.
My recommendation: you should turn towards novels. There are a couple of really good novels on Tapas (e.g. Looking for Derek). I think novels are the only option you have if you want to read something that talks about the gay community in a deeper way.