"I relate to Lindsay [Lohan]," Wahler tells PEOPLE in its new issue, "because she's the same age as I am. I'm only 20. And to say that I can't drink ever again – even on my 21st birthday – is hard. But I don't care, as long as I'm healthy and happy."
Those weren't always his priorities. "Anyone who's big in Hollywood who's underage gets in [to clubs]," he says.
Armed with a fake ID that he wasn't even asked for, by 18 Wahler had graduated from occasional social drinker to someone who partied hard three or four nights a week – a situation he considered normal, "until I started becoming someone I'm truly not," he says.
"I did try drugs, but it was never my thing. It was alcohol, for sure. It would take me about 10 drinks before that other side came out. It's like Dr. Jekyll and Mr. Hyde."
A scuffle with an L.A. tow-truck driver in September 2006 led to a conviction on misdemeanor battery charges. And after allegedly punching a Seattle hotel security guard in the face on April 8, he was charged with criminal trespassing and assault.
"I'm embarrassed as hell, but I really do not remember my arrests," he says. "They're blackouts. And that's scary."
Coral Von Zumwalt
Wahler – who's now dating tennis player Katja Decker-Sadowski – says of the rigorous regimen at Chapman House: "It's exhausting, but after I started getting back to my senses, it was cool to get up in the morning and not be all hurting."
For more about Wahler's struggles with alcohol and his first failed attempt at rehab, check out this week's PEOPLE, on newsstands Friday.