For how long will you get herpes simplex 1 after you have been exposed to it (had sex with someone with it)?

Usually a few days. If you mean time until symptoms start, it's usually 2-5 days, rarely up to 2-3 weeks. If no blisters or sores by 10 days, you're probably in the clear. But low chance of infection from a single oral sex event. If you mean duration of HSV1 once infected, it's forever. Herpes infections persist for life. But for genital HSV-1, outbreaks and transmission to new partners usually are rare.