EXCLUSIVE

"90 Day Fiance" star Colt Johnson told cops Larissa Dos Santos Lima downed half a bottle of pills and threatened to kill herself before getting arrested.

TMZ broke the story ... Larissa was arrested for battery last week after she allegedly attacked Colt, punching him in the mouth and inflicting injuries upon herself. According to the police report -- obtained by TMZ -- Larissa got mad at Colt, accusing him of cheating after she discovered he'd purchased porn.

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Cops say Colt told them Larissa became enraged, and emptied her bottle of antidepressants -- which was half full -- swallowed the pills and locked herself in the bathroom. She also punched Colt in the mouth.

According to Larissa, she locked herself into the bathroom to defuse the situation and took a shower. She told cops during her shower, Colt was playing with the lights and continued to annoy her by touching her inappropriately. Larissa also claimed Colt grabbed her by the hair and pinned her to the ground.

After talking with both Colt and Larissa, cops discovered Larissa had been busted for domestic violence twice in the last 6 months. They also determined she'd inflicted scratch marks on herself.