Getting to your questions:
- Chlamydia is serious for a small proportion of people. Many people clear the virus after a period of time, but not if you are having ongoing sex with someone with it! A low chance of issues, but get checked out.
- Most women are asymptomatic with chlamydia, less so men. Some men experience stinging pee (especially when they start a stream!) and this is often within a few weeks of infection yes.
I'm afraid I would go with the view that your partner has had sex with an infected female recently. Your chances of having chlamydia are bordering 100% as transmission per sexual episode is 30% or so. If you do not have chlamydia, then your partner's infection is really recent!
Regardless, with your test result, you and your partner need to sit down and discuss. Put on him you need to know the truth of what he has done, broad reasons why and what does he think it means to your relationship going forward. Don't get stuck in details of how many times, how did he meet her etc. it won't help.