How can my boyfriend test positive for chlamydia and i tested negative ?

Chlamydia test: This situation is pretty common. The tests aren’t perfect, and miss a few infections; you may be infected despite your negative test. Your partner’s test may have been false (rare). The immune system clears chlamydia over time, even without treatment; you may have had it but no longer. Or he caught it from someone else and you didn’t catch it yet. You should assume you have it and get treated.