what the hell!!

So I have only just found out my meant to be partner never told me he had caught cylmidia off a girl he slept with (he has gotten rid of it and this was before me) but he never told me his step brother did and honestly I am so freaked out I know obviously I have to go get tested to be all clear but what the hell he never told me anything at all ever!!! I'm actually so angry and don't even know what to think I want to leave him because it really has turned me really off... 
Has anyone else ever been in a similar situation and what did you do 😩