If his immune system is compromised, rare complications can happen with Herpes. Did you get it from him? If you did, then there isn't really anything to be done about it.

Regardless of his health status, if you didn't get it from him, you need to use protection every time you have sex to keep from spreading it. You can spread it whether you are symptomatic or not. Have you asked the doctor about medication for Herpes to keep you from getting an outbreak?

Also, I'm so sorry to hear about your boyfriend's cancer. I hope he is getting the best care and everything turns out well. Luckily Hodgkin's is very treatable. I wish you both the best.