Had sex with 2 people, found out i had chlamydia, got treated. went back to one of the people again, could he 100% pass it back to me?

Here are some...: Make sure your partners being evaluated, tested, and treated as needed before resuming sex activities with the same persons or any known infected. As to 100% for something, it is known nothing is 100% in real life. For STD transmission, exposure doesn't mean contracting and contracting doesn't mean becoming clinically infected. So, evaluation, treatment, and timely follow-up are essential in care

Yes if not treated: If that partner received a recommended treatment, he probably was cured and cannot pass it back to you. If he was not treated, then absolulte yes: you WILL be reinfected. And second chlamydial infections are especially dangerous, with a much higher risk of pelvic inflammatory disease (PID, tube infection) which can make women sterile. Don't take the chance!