"I’ve been doing horrible and I realize that now and I’m doing everything I can to change it."

That's "Mayhem" Miller getting real with his thousands of followers ... sharing he's been seriously struggling after years of bad behavior that often left him in handcuffs and behind bars.

But, the 42-year-old retired MMA fighter is vowing to change his life for the better.

"I went away for a couple of years to pay my debt to society, and when I got out, I realized that I have much more paying to do," Mayhem wrote on social media.

He continued ... "I thought I could smoothly transition from prison to the regular world, but things have been more difficult than I imagined, especially interpersonal relationships and the burden of being free."

Of course, Jason has been in an almost constant state of legal trouble over the years ... getting arrested for everything from fighting in bars to allegedly choking a fan in August 2023. He's been in and out of jail.

Mayhem isn't looking to go back, though ... and is now opening up about asking for help, something he wasn't willing to do in the past.

"Until recently I viewed asking for help as something for the weak, but a very special person has shown me that the actual opposite is true; asking for help shows strength. Strength of character and strength of mind."

Miller also offered a heartfelt apology to his family ... for what they've been through.

"My family has bore the brunt of my frustration and self destructive behavior, so to them I offer a sincere apology and if I have directly affected you in a negative manner, I am sorry."

Mayhem, who beat beasts like Tim Kennedy and Robbie Lawler during his fighting career, says he now plans to step away from social media and his everyday routine and work on himself.

"I’ve been doing horrible and I realize that now and I’m doing everything I can to change it. Thank you for your support, but I’m not reading comments. I’m going to work on me now for the good of my family."