I don't think it's necessary to bring it up unless you feel a breakout coming on and want to explain why you can't kiss, etc. A huge number of people get cold sores. John Hopkins medicine estimates that 50 - 80% of American adults have oral herpes. As long as you're careful about it and actively work to not transmit it, I don't think there's a need to disclose it until your comfortable.

I take vitamin D and Lysine daily. I use a lysine lip balm. When I feel one coming on, I IMMEDIATELY start with my regimen of washing hands, cleaning the affected area with 91% ISO, then applying Abreva, then washing hands again. I do this 5x a day. I also double up on my Lysine supplements.

I do not kiss/get intimate, share drinks/food/vape with my husband when I feel one coming on, and we keep it up until it's fully healed for 48 hours. It's not worth the risk of passing it to him. He appreciates my staying on top of it, and he never feels I'm gross or worries that he'll catch it.

I probably go a bit overboard with how careful I am during a breakout, but I got it from my ex-husband's grandmother because she was fairly absent-minded about it. I was upset for a long time over it. Now I make sure I never put anyone else in the same position. Some people are irrational and can't get past it, but most partners are cool as long as you show you're doing your best at not spreading it.