What happens to a boy when chlamydia is untreated, and what happens to the girl when chlamydia in untreated?

Several problems. Most infections aren't serious, but don't take the chance; get tested and treated if possibly exposed. Chlamydia is one of the most common causes of fallopian tube infection and female infertility. Serious outcomes are rare in males, but still can occur, especially painful testicular infection (epididymitis). Occasional reactive arthritis, which can be quite serious, in either sex.
Many things. There may be scarring and infertility. Chronic severe infection can occur. The male may not have so much of a problem but the female can. Please see someone if this is your case and get approppriate treamtment and follow up.