Have safe sex and take your anti-virals is the only advice I can think of. This would apply even if he didn't have a suppressed immune system. I hope that he already knows about
the herpes, so you being together has got to be important to him. I can't say I know everything about
Humira and viral infections, having not had the joy of having to take biologics yet, but just like anyone else, the worst that would happen is that he catches it, perhaps has some more outbreaks than a person with a typical immune system, and he'll have to start on anti-virals as well.
The doctor would have not recommended anything that had potential to cause illness.
Perhaps some alternative sexual methods could be experimented with during his treatment?
Best of luck! It sounds like a potentially scary situation... but if you let this little thing take the joy out of your relationship it won't help either of you. He needs your support and strength, not more stress and anxiety.