Pregnancy after protected ?

I had unprotected with my significant other several times within a 2 week period, but also had protected with another guy once, then had unprotected with my s/o 2 days later. The possible dates of conception are a little close for me to find out exactly, but what are the chances of me being pregnant after having protected once? the condom didn't appear to break and we didn't notice any leakage. I'm worried!