Chlamydia and pregnancy...

I got a call from my OB today telling me that I have chlamydia and that my SO and I need to be treated. But I've never had an STD before and I did not cheat on my SO. I'm worried about how this will effect my unborn baby and my relationship with my husband. I just don't know how long I had it or if my SO could have given it to me from his ex without us knowing he had it.