Dark Heaven
This is top. tier. shit. It's way more than just a simple love story, it has one hell of an amazing plot. So much drama, while also being good representation and dealing with subjects like homophobia and racism in society. But at the same time it is so cute and of course an incredible and beautiful romance along the way. It's quite a journey. Cried many times, and a piece of me is gone now that it is over. AAH!!
Itoshi no Nekokke
How can it get any better than this? The manga seems like basically a slice of life, but the world built in it is so immense. We see the life story of this couple. The sad moments growing up, the fun moments of living in a sharehouse, and the extremely adorable fluffy moments of just being a couple. But it never gets tiring--nobody can write characters with such personality, chemistry, and realism like this author.
Portrait (natsume Kazuki)