If you have gential herpes can you have sex with someone if you don't have an outbreak or any symptoms of an outbreak without passing it on to someone else? or will they still catch it?

Yes, transmission definitely can occur in absence of a visible outbreak, especially when genital herpes is due to HSV2; the risk is lower for HSV1. If you have HSV2, you can reduce that risk by daily treatment with acyclovir or valacyclovir; and the combination of that treatment plus consistent condom use is very effective in protecting partners. Even then, however, the risk is not zero.