We can't tell you how to handle this.
Withholding the truth can be a huge betrayal of trust. Countless women on here have been driven to distraction by lies and deceit from their partners, even when they have corroborating evidence. To deny under those circumstances is suggestive of an appalling lack of respect for your partner.
In your case it appears that your partner has no suspicions whatsoever, however, which would make your confession much more about guilt than it would about respect for his feelings, making it more of a selfish act rather than a noble one.
The trouble is, you're not your partner, so you can't guess how you'd feel in his position.
He may prefer not to know because while not knowing he can continue with the happy marriage and not have that lingering doubt or fear. This is why some people manage to ignore evidence for affairs; they don't want to know because they don't want to change their lifestyle for whatever reason.
Alternatively, he could decide that he wants to know because anything less than full disclosure is living a lie.
He could refuse to stay with you or he could be devastated but choose to work through it (odds are less likely when the female has the affair however, be warned).
There are too many variables out of your control here. You can't know what's right for your DH because you're not him. In a way, assuming that you'd know what someone would want and acting accordingly is a strange form of arrogance. With so many variables, I'd say you have no choice but to be guided by your own conscience and what you want.