PK's ex before Marl discouraged her to draw porn but she broke up with him for not enabling her. She wanted to do this so she hung out with people who had the same interests. Eevee is around the same age.
If you think Marl is this predatory mastermind who groomed poor innocent PK, you're falling into the narrative they want you to believe.
I don't think Marl was any mastermind, But I was fairly sure she was dating Marl when she did her cub-comic with the flower-kitties which she did admit she was underage to do - but I don't figure it was actually malicious.
Marl suited her because he encouraged her to keep drawing lewd things and was slightly older. Plus was in a position to get his own place quicker, to PK that would of been the main thing - getting away from being bounced around family.
He probably did genuinely love her, but for PK it was more about getting away from her childhood completely and starting over. She found she had feelings for Eevee, but he wasn't old enough to provide the home she needed. Marl decided to tolerate the situation, but declared Eevee had no business in their home so it was visits only. Eventually Eevee was old enough and making enough money to turn the tables - somehow PK convinced Marl to move to a place Eevee owned and that seemed to cement his third wheel status.
Marl from that point was number 3, he didn't own the house, he wasn't top dog (lol) in the relationship anymore and he seemed to be the guy who managed cooking and did the admin for PK's business while PK and Eevee's days consisted of getting up, moving to the computer, and relying on Marl to feed and do non-computer admin for them.
He thought this was a better long term plan than say, admitting he had long lost the battle and finding someone who wouldn't treat him like a glorified skivvy.
He's still a slime but one wonders if his life and mental state will improve tenfold away from PK and Vee - assuming it's true and he doesn't give in to his worst impulses anyway.
