"When I knew it was done and when I knew I'd tried my hardest and when I knew there was nothing more I could do, then I could leave," Maci, 19, tells PEOPLE as part of its Teen Mom cover story. "It finally got to that point."
But now, Maci says the two are "doing a very good job" co-parenting their 22-month-old son, despite the fact that both are in new relationships.
"We've had our ups and downs where he wants this and I want this, and just stuff like that, but the only thing we talk about and the only problems we have are about Bentley," she says.
Parenting ChallengesStill, their relationship is far from perfect. In this season of the hit MTV reality series, viewers watched Maci bring Ryan to court to demand child support. "Ryan really does try to be as difficult as possible," she says. "I just think that he wanted it in writing to know that he was paying. So he wasn't going to pay me without it being noted so that there's proof."
"Now [Bentley] is excited to see him or he's sad to leave him," she says. "If he sees a truck that looks like Ryan's, he'll say, 'Da-da.' There's an emotional connection there that wasn't there before."
Another influential man in her son's life? Maci's boyfriend of eight months, Kyle King, who has yet to meet Ryan.
"For a while, Kyle acted more like a father than Ryan did," she says. "He'll want to put him to bed, or put his pajamas on him, stuff like that. Stuff that I was used to doing by myself. I was just like, 'Are you supposed to do that? Is this how it works?' So it's strange, but it's really, really good."
For much more on Teen Mom stars – including our story with Catelynn and Tyler – pick up this week's new issue of PEOPLE, on newsstands now