Matt Baier tells PEOPLE he has "a lot of shame" over outbursts he had while filming — several of which he cannot remember because he was under the influence

Amber Portwood‘s fiancé Matt Baier is coming clean and wants to explain the reasoning behind his infamous meltdown in Las Vegas.

The Teen Mom OG star is exclusively revealing to PEOPLE that he suffered a relapse this year while filming the current season of the hit MTV show.

“I had a drug relapse this year for the first time with prescription pills. I fell back into my addiction for about two months around December,” Baier says. “I was taking a good amount of pills and I was killing the pain. Before I knew it I was back in the cycle again and completely off my program. I was still convincing myself that it wasn’t as bad as it used to be but it was.”

The 46-year-old recovering addict says that he was using at the time cameras filmed his freakout during a friend’s Las Vegas wedding. (The episode aired on Monday).

During the episode, Baier was looking at Las Vegas wedding venues with friends and tried to convince Portwood to elope, but she refused, launching Baier into a vicious tirade. He flipped out and told an MTV producer he was “done” with his relationship with Portwood.

“She wants to marry her brother. F— her,” he said on camera. “She just humiliated me on TV. I’m done! Done.”

Credit: MTV

The drama continued into lunch, when Baier, who was seated with Portwood and her friends, left the table to tell a producer, “I will fake this for the rest of the day. But I am done with her f—ing psycho ass … I will not marry her now. I will not marry her ever. I’m not gonna let her brother dictate my life,”

After seeing the footage, Baier says he broke down crying knowing that his relapse lead to the meltdown — a meltdown he didn’t even remember because he had blacked out.

“That person that I was watching was not me, it’s not who I am,” he says. “I remember getting really upset and I felt a lot of shame. Also, what I said is completely not how I feel and it also didn’t make sense. I do know that I allowed myself to have my buttons pushed that day, I just don’t remember it all that well. They just caught me on a really bad day.”

“When I saw that piece of tape I had no idea that even existed — that wasn’t me,” Baier continues. “I completely blacked out. I was selfish. I was rambling. I was not remembering something we had filmed just 20 minutes prior. I was in a really, really bad place.”

That wasn’t the only time Baier blacked out from taking too many prescription pills.

“The last time I took pills was roughly around four months ago when I was in New York. That was a big slap in the face. We went out for a press day for a couple days and after we finished the trip we went to L.A. to film something. [While there] I saw one of the Teen Mom executives and I asked them a question.”

“He looked at me and said, ‘Matt, we had a two-hour conversation about this already.’ I didn’t remember the conversation or even seeing him in New York,” Baier continues. “I barely remembered the trip. That was the turning point for me, I had just blacked out an entire two-day trip, I have a problem again.”

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Baier also admits that while all this was going on, he tried to keep Portwood, 27, in the dark about his relapse.

“At first, Amber did not know about it, because I did everything I could to keep it away from her. That lasted a very short time,” he says. “She came to me concerned and said, ‘Look, we’ve been together for three years, I know you better than anybody, you need to tell me what’s going on.’ “

“One thing I can’t do is lie to Amber, so I said listen, ‘I’m in a bad place.’ She told me to get help immediately and you need to get back on your program,” Baier adds. “She really kind of got in my face about it. I was afraid at first to tell her, you just never know how people are going to react. Amber is supportive, but she can be stern when it comes to stuff like this — she was pretty firm about it.”

Now with Portwood involved and expressing her concern, Baier knew the next step would be to call his sponsor and get back on the program. One thing Baier insist on, is that he wasn’t using when Leah (Portwood’s 8-year-old daughter who’s from her previous relationship with Gary Shirley) was around.

“I did not use when we had Leah. I would never. I never did drugs around my kids,” he says. “Having Leah around was one of the best things that ever happened to me because it preoccupied my mind. I had to take care of her and I didn’t have to think about all the negative stuff.”

Though his thoroughly disappointed in himself for relapsing, Baier sees a silver lining.

“I got sick afterward after I went to my program [for the first time since relapsing]. I threw up for a few days, which I needed. I needed a reminder that this isn’t a life I wanted,” he says. “I would never want to go back to this life. I spent a lot of years sober and I was disappointed and ashamed that this happened but I am also going to grow from it. Now I have zero desire for it.”

Teen Mom OG airs Mondays (9 p.m. ET) on MTV and Baier’s new tell-all, You Have No F–king Idea: The Naked Truth About My Life, is available June 6.