During Tuesday's episode, Portwood, 31, became emotional and walked off stage after learning that her 12-year-old daughter had been attending therapy sessions without her knowledge.
"She is speaking to somebody, a professional," Portwood's ex Gary Shirley said. "You probably didn't know this. Per Leah's request, she didn't want it to be talked about. I have permission to talk about it and to make it known."
Shirley then explained the teenager didn't "want anybody knowing."
"I supported that," he continued. "I was like, 'It's your safe spot.' They're working on different things that she can do to help the communication start between her mom and her. ... She's gone, I think, about 10 [times]."
But Portwood wasn't pleased that Shirley failed to "communicate" with her and withheld information about her daughter from her.
"Here's the thing, I'm the mother. I need to understand what Leah is going through, so I believe the communication should be there for that," she said. "I also think that Leah is a child. She is not an adult. She doesn't need to say anything, but you can tell me."
Shirley argued that telling Portwood would "break" Leah's trust, to which the MTV veteran disagreed.
"She wasn't wanting to go unless she felt safe and had somewhere safe to say what she wants. I was trying to let you know," Shirley said as Portwood replied, "Well, thank you for letting me know on the stage here. I don't need a camera in front of my face for me to know something."
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Portwood called Shirley "garbage" for disclosing the therapy information on-camera, resulting in her promptly walking off off the reunion stage.
"You came out here with some bull crap. I just found out on camera, of course. Everything that you do is for television. Done!" she said. "Everything that he does is for television. I'm out. Bye! I'm not for it."
Portwood and Leah have struggled with their relationship over the years. Previously, Portwood — who also shares 3-year-old son James with ex Andrew Glennon — said she would be interested in having Leah go to therapy.
"It truly breaks my heart that Leah and I are drifting apart," she said on Teen Mom OG in September. "For the past six years, I've been seeing a psychiatrist. I really think if I could go to therapy with Leah, it would bring us closer together. But Gary and [his wife] Kristina [Anderson] feel differently."
After the reunion was filmed, Portwood opened up to Page Six on about her current relationship with Leah, saying things are "so much better" between them.
"I don't want to mess anything up, but [things are] good," she added. "She's reaching [out] and I am [so excited]. My arms are up and open."
Teen Mom OG airs Tuesday nights at 8 p.m. on MTV.