I have an antibiotic for my strep throat but if my partner sleeps in the same bed as me is he likely to get it too?

PERHAPS: Avoiding close contact such as kissing and careful attention to handwashing should significantly reduce the risk.

Likely: You are contagiousness for 24 h after you start an antibiotics. You could have infect you partner before you knew you are sick. The incubation period is 7-10 days, so you will know soon if you infected your partner. Universal precaution is the best think you can do while you are sick and try not infect your friends and family.