I'm so sorry I don't have much time atm, but if he's being truthful about all that has happened, I see this situation as very hopeful.
It must have been a horrible bombshell, but your H clearly has some investment in your marriage to have told you this now - and about his earlier indiscretion - before letting this go too far.
It's also not surprising that he says at the moment that he doesn't know what he wants, because this is still so new. What he is also telling you that this isn't about your marriage, but about a yearning in him, also sounds truthful.
I suspect that your H has an individual vulnerability to new beginnings; the thrill and excitement of a new relationship, but doesn't necessarily want to threaten his marriage. Of course this does threaten your marriage and it needs resolving.
Do please read Not Just Friends but in the meantime have a look here and read the introduction. Click around the site too - it's very helpful.
In your shoes, I would absolutely insist on talking. Despite your shock and hurt, the one thing I would make sure I said was to thank him at least for raising this with you now, because a crush and a kiss is surmountable, although there will be lots of work ahead.