Well, you have information that you are keeping from your life partner. This information is important and may cause your SO to make different choices or act differently. This information is very pertinent and relevant to the relationship. IMO, if you don’t confess, you have not only cheated on your spouse, but you are lying each day you don’t tell. You are also denying your spouse the things you probably promised in your vows, and I think the spouse has a right to know that the marriage isn’t (or hasn’t been in the past) as he/she thinks it is.
I think deciding for your spouse that they’d be better off knowing, is not only arrogant and self-serving, but the marriage is under false pretenses from that moment forward.
If I found my spouse had cheated on me, I think (can’t know until I’m in that position) that I might be willing to try and work past it. If my SO cheated on me, and lied, covering it up, and I found out anyway, there would be no hope for the relationship. Once-off cheating I think I could deal with, as long as we took the time and the counselling to do so. Lying to me each day, by not telling me about the cheating, I couldn’t accept. One bad choice can be forgiven IMO, but continual and planned deception is another story.
IMHO only & YMMV, of course.