I'm sorry to say, ThreeTimes, that from what you are saying here that is exactly what you are in for.
You don't get it, OP. You really don't.
IF YOU TELL THEM, IT WILL BE THE SAME. All that will happen is everyone involved will be incredibly hurt and destroyed and then you will wait, taking absolutely no responsibility for the next stage, waiting to see what they will 'do' or what they 'want'. And you will talk to your lover about what is happening with each of you and they partners will maybe say they still want it to work, so you will try, but the marriage will be so damaged by the revelation that you will perceive the marriage to be even weaker now (WHICH IT WILL BE BECAUSE OF WHAT YOU'VE DONE) and so you'll keep returning to your lover to see if maybe you should have actually left when you told them and you will share what's going wrong with the rebuild on both sides, but not be able to leave because you promised to 'try' and by maintaining contact you will scupper the marriage being rebuilt and by hedging, timing and cowardice you will scupper getting together with OM AND IT WILL GO ON FOR FUCKING EVER BECAUSE YOU NEVER HAD THE COURAGE TO MAKE AN ACTUAL DECISION BUT JUST CHUCKED THE BOMB OF YOUR BETRAYAL INTO MANY PEOPLE'S LIVES AND THEN RAN AWAY WITHOUT MAKING ANY SORT OF DECISION.
Your passivity, hand-wringing and priorities here speak so so badly of you, OP. I'm sorry, I know you're in pain but you have to listen to me when I say you hold the lives of so many people in your hands right now and you are treating it so foolishly and lazily.
WHAT DO YOU WANT?! seriously. 'You have been thinking about telling your own DH'??!! Really? how noble of you.
Decide what you want to do, then commit to it and tell the people the truth about it. Read WHEN GOOD PEOPLE HAVE AFFAIRS if you want hand holding by someone sympathetic through it and what you should do.
But do not come here looking for sympathy for a plan like that. Destroying lives just because you are sick of you how you're own massive betrayal has impacted YOU and you want someone else to make your mind up for you. Jesus Christ.