Adrien knew what it was like to have a broken family. It was only after his mother disappeared, he noticed how strained his parents' relationship had become, terse conversations, passive-aggressive agreements, bitter lonely meals three times a day. His strict schedule and modelling being tiring on top of that
Not to mention his cousin, who he once was quite close to, was cold and distant now. And his aunt constantly demanding the heirloom rings every time she spoke on the phone or visited.
Luka knew what it was like too. He never knew his father until an akuma attack, his mother was as rebellious as, well, a pirate, and his severely anxious sister, Luka had a lot on his mind.
He also had to worry about his pizza delivery job, the bills to be paid and Kitty Section rehearsals and performances. His mother's job didn't pay as well as they hoped it would. He had a lot on his plate as well.
Fortunately for both of them, they both have been seeing a therapist help them with their issues. Adrien said to his father it would be helpful for the loss of his mother, going every month, and Luka set a small number of his wages aside to pay for his monthly appointments.
Coincidentally, they had the same therapist, and Luka's appointments were always an hour after Adrien's.
They always sat beside each other in the waiting room, chatting about their lives, their struggles and found they related to each other a lot.
Luka began coming an hour early to his appointments, just to spend time with Adrien. He never minded the wait afterwards.