Actually I don't quite understand this manga, maybe because I don't remember all that happ...

Is there something specific you don't get about them? Or just in general?

Their relationship is just less intense than that of young people. They don't have all these grand gestures and confessions because they've grown up and faced many things already. One had to care for his aging and ill father, meanwhile unable to truly rest. The other had been facing burn out and stress to the point of complete exhaustion, losing his motivation to keep going. Then they found each other again, and just fell into a comfortable rhythm as they worked together. They weren't officially a couple because the feelings weren't all there yet, but they became close friends. Since then they've been each other's rock, and although things have changed, they have maintained their friendship. To some degree they didn't really need to say "I love you" but they did begin to notice a shift with feelings of jealousy and wanting to remain together. And now it's basically confirmed they love each other, but it's clear their relationship has been more that of partners for a while although they haven't said the words. Others have also noticed their closeness and perhaps see them as a couple despite how they haven't confirmed anything up until now.

It’s drama free, slice of life, friends to lovers, older lovers

Thanku so much this helped me a lot, cause the dynamic seemed weird at first, just didn't get it, now it's understandable

No problem! This story in itself is a bit of an enigma because of how mellow the characters are. There is some drama, but it's not the same like in other stories where one would feel betrayed and stew in his emotions until it all exploded. The MC despite feeling jealous was mature about it, he didn't try to cling on to the ML or sulk about it without discussing anything. They talked it out.

They also aren't afraid of just being on their own. Other stories would make it a big deal that they spend weeks apart without contact, but for them it's not bad. They have their own lives and work, they can't realistically be attached without living together. But they talk about important things, they discuss what's happening in their lives, and they spend valuable time together (including vacations and holidays).

Yea, I think the more I read it the more I'll appreciate it^^