Everything I've heard points towards Herpes being not that big of a deal as long as you're careful UNLESS you are a woman who wants to have kids. Having an outbreak while pregnant/giving birth can cause issues (although they are usually VERY prepared for what can happen).
So, I'm not sure on your age/family status but if you and your wife plan on having a(nother) kid, you might want to look that aspect up before deciding to be physically intimate with your secondary. Either way, I don't think the relationship has to end just because you can't/won't have sex.
Talk to a doctor, keep talking to your wife, talk to your girlfriend... Just make sure you've thought out all the possibilities before making a decision that could affect you and your loved ones forever.