Well, "greatly endangered his health" is an overstatement. While genital herpes is to be avoided whenever possible, it's not a particularly serious health threat!
The reply to follow assumes your self diagnosis is correct -- which it probably is if you have had recurrent oral herpes in the past and your current recurrence is typical. If this is a new experience for you, then before being too concerned about your partner, see a health care provider to confirm your presumed diagnosis.
OK, assuming you were having a fresh oral herpes outbreak when you performed oral se on your partner, there is probably a 50-50 chance he isn't susceptible and will not get infected. About half the adult population of the US (more in most countries) is infected with HSV-1, usually dating to childhood; those people are immune, or at least highly resistant, to catching a new HSV-1 infection. (HSV-2 isn't a concern here, since it is a very rare cause of recurrent oral herpes.)
If your partner has not previously been infected with HSV-1, then there's a pretty good chance he could catch it from the exposure you describe. However, there are no data to estimate the actual risk. Probably it' somewhere in the range of a 10% to 50% chance, but even those figures are just an educated guess.
Unfortunately, there are no measures to be taken at this point except to watch for symptoms of genital herpes (penile blisters/sores) and for your partner to promtly seek medical care if they develop. Taking an antiherpetic drug like acyclovir or valacyclovir before symptoms develop won't prevent infection; research in animals shows that unless the drug is taken within an hour of exposure, it has no effect in preventing infection. And treatment could confuse things, by delaying symptoms, making them atypical, and otherwise interfering with knowing whether infection occurred. So at this point it's best to just wait for symptoms and hope they don't occur.
As an option, your partner could see a health care provider now and be tested for antibody to HSV-1. If the result is positive, he will know he was infected previously and that there was no risk from this event -- and no reason to be worried about future oral sex between you.
If the worst happens and the infection was transmitted, it is very unlikely your partner will have "a lifelong battle with herpes". Among people with newly acquired genital herpes due to HSV-1, about 40% have only the initial infection and no recurrent outbreaks at all. Another 40% have 1-2 outbreaks in the next couple of years, then no more. And only a few have frequent ongoing recurrent outbreaks.
Presumably you have spoken to your partner and he is aware of the situation. If not, you need to do that immediately so he can participate in discussing the issues and options I just outlined. But the bottom line is that the risks and outcomes are not as dire as you initially thought.
I hope this helps. Best wishes-- HHH, MD
A related discussion, Oral sex and cold sores was started.