'Love Is Blind' John Shannon Admits to Cheating on Wife Sarah Williams With Stripper

"Love Is Blind" star John Shannon is coming clean about what ultimately destroyed his marriage to Sarah Williams ... admitting he crossed the line with a stripper who also worked as an escort.

During Sunday's Season 11 reunion, John finally gave more details about the incident that led to the couple's split, revealing it happened during a boys' night out about six months earlier.

John insisted nothing physical happened, but acknowledged he crossed a boundary Sarah had established in their marriage. He also admitted he later exchanged inappropriate text messages with the woman he met that night.

Host Nick Lachey eventually pressed John for a straightforward answer, asking whether he considered his actions cheating. John conceded ... "I guess so, huh? Yeah."

John later revealed the woman was a stripper who also worked as an escort, explaining she gave him her phone number and he reached out afterward. He maintained nothing happened between them physically.

Sarah, meanwhile, said the messages were a major betrayal and ultimately gave her the push to walk away from the marriage. She also opened up about struggling with John's communication style throughout their relationship ... claiming he frequently insulted her and made hurtful comments.

John took responsibility for the breakup, saying it was 100% his fault and admitting he was devastated by how things turned out. He also said he's been working on himself in therapy.