"In my situation, I felt in the program there were a lot of eyes on me. And it was very uncomfortable. I was not using my anti-psych medication even," the 22-year-old reality TV star explained.
"You know, I was very depressed, all alone, all bitter at everybody. I felt like that wasn't the life I wanted to live, I felt like I'd rather do my time, and get it over with, and make the best out of the situation that's been handed to me."
Portwood will receive credit for time she has already served in jail, however, she is still likely to serve at least two and a half years in prison even with time off for good behavior, according to authorities.
Portwood refused to finish the rehab program after participating for three months, but claims there was more to her decision than people may assume.
"It wasn't just the program," Portwood told GMA. "It was the fact of being alone. It was personal. You know being alone, feeling like you're hopeless, you have nothing, feeling like an addict and you're never going to change, even though in your mind you're working so hard but every time you get to court it's not good enough."
Portwood apparently struggled to stay clean during her months of treatment and just finally reached the point in May where she felt the need to give up and go to prison instead.
"You want to be free. Who doesn't? But you know if you can't do it, if you can't do it, why are you kidding yourself?" Portwood said, adding that she plans to use her time in prison wisely.
"I'm going to take some classes, I'm going to get my GED, take as many programs as I can. You know, just try to better myself for when I do get out and not stay in prison... I'll be off the drugs, I'll have an education to get me a job. You have to think of the positives in this negative story."
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And while Portwood insisted her issues don't directly stem from starring on Teen Mom, she said the fame and fortune contributed to her downfall.
"Getting money at a young age, going to parties where drugs were given to you, that's what really got me... You make your own choices," Portwood told GMA.
"It's like every time you go out to eat, you know, people are staring at you, talking, and it's hard. You get paranoid... It's not normal, to always be paranoid."