Preferably with a female lead, but male is fine. It would be nice if the character's ages ranged from their early twenties to mid thirties. Sex or nudity is fine, just not straight up hentai. Also okay with manga that deals with darker subjects. Thank you.

Examples:
- Beloved (Jaeliu)
- Bitter Virgin --Not quite sure if this fits it's been a while since I read it.
- Cat Street
- Coffee & Vanilla
- Hapi Mari --I think I've tried to read this like 5 times already =_=
- Imagine 29 --Only read chapter 1 but it seems promising
- Ohmi Tomu's mangas --Kinda bad tbh
- Oyasumi Pun Pun --Not sure if it fits. Didn't enjoy.
- Real Clothes

Toukyou Tarareba Musume - Can be quite comedic, but deals with the struggles of unmarried women ages 25-40 and the fear of ending up alone.

Solanin - Same author as Oyasumi Punpun, but is much more realistic with a female lead. One of my favorite "life" manga. Deals with the struggles of mental health and the struggles of finding purpose.

Natsu no Zenjitsu - Has a male lead and there are sex scenes that can be quite explicit, but it isn't bad. It's actually quite tasteful/realistic. Contains heartbreak.

Kasane (MATSUURA Daruma) - Female lead. There's a fantasy aspect to this one, and romance is only sprinkled here and there, but it's quite an enjoyable read. Can be super dark with heartbreak, betrayal, death, etc.

I'd also suggest 3 Level Combination, Koibito Play and Octave.

And yeah, a second on Natsu no Zenjitsu.

Haru no Noroi is one of the more darker themed manga regarding relationships that I have read. Definitely at the top of my list, as the main character's raw and heartwrenching emotions could physically be felt. Deals with the aftermath of a tragedy, and the relationships that come about because of it.

Watashitachi no Shiawase na Jikan tears at your heartstrings. Contains some heavy topics such as suicide and depression, but shows the bonds that two broken people can have. Beware the tragedy tag however, it is quite the tearjerker.

Sekine-kun no Koi featuring a male protagonist, but doesn't shy away from topics such as sexual abuse and rape. Also highly recommended as you soon find yourself rooting for him in his struggle to fill the void created by his past.

Thanks guys. 😁

Honey and Clover, lead is male though.

Maybe Toukyou Tarareba Musume? It deals with the subject in a sardonic/irreverent manner so may not be what you’re looking for.

I second Solanin, even if you didn't enjoy Oyasumi PunPun. It's much more subdued (and less dark) so I would still give it a shot. Tokyo Tareba Musume is good if you don't mind something more comedic.

Futago
Kabocha to Mayonnaise
Udon no Onna
Watashi ga Itemo Inakutemo
Cousin

Thanks for the replies, I'll be sure to check these out.