Long time since I've been here, but wanted to chime in.

I think it is about YOUR story, YOUR life.  Your exGID partner did not have a right to prevent you from telling your narrative.  I agree with Lily, this allows him to control the narrative.  

I told 2 of my sons that I suspected their father was gay and it was such a shock and so difficult for them, but I had a GIDX who was spewing platitudes about growing apart when it was more like a bomb going off in my life.  I was devastated and only wish I had done it in a more well timed way.  I would now sit them down individually and have a calm and measured conversation in a relaxed setting. 

I goofed (humans right!) and my disclosure to them was in an off the cuff moment where I was feeling triggered by a comment one of my son's made about their father's narrative.   

Wishing you luck and yes so well done to hold fire until he was 18....both my sons were adults when I told them.  

I told my daughter after D-day but before I'd made any decisions about whether or not to leave the marriage.  I felt like there was just too much lying in the family, that it had affected everyone -- including her -- and that I'd gotten to the point where I was speculating like crazy about whether she'd already guessed.  So I had to put my foot down and say "no more secrets in this family."  

I'm so sorry your divorce decree prohibited you from being honest within the family.  In addition to being the ex-wife of a gay man, I'm also a lawyer and the more I see of these nondisparagement clauses, the more I'm convinced they're a disasterous idea that somehow became normalized a long time ago -- and nobody has ever revisited the idea of whether they're really doing far more harm than good.

I agree that you should tell your son, but do so in a way that he won't defensively take his father's side.  You might say something to the effect of how you had learned of his father's sexuality and you realized that this situation was untenable -- not only for you, but for your husband as well.  You can tell your son the divorce decree has barred you from discussing this with him until he turned 18, but at this point there is nothing healthy about a family in which secrecy and lying is the norm.  

After I was browbeaten from telling our adult son the truth, which I wanted to do because I wanted an honest relationship with him, I honored my ex’s request to go with the “we’re happier apart” nonsense. I did later tell our adult son people don’t divorce after 35 years for frivolous reasons.”  I told him there was an issue of his father’s, that he could ask his father about it, but that I already knew his father wouldn’t tell him ( he’d told me he would say “some things are private”), but that I would tell him ( my son) if he wanted to know. He said he didn’t, so I didn’t.  When my ex got involved with another woman, I told her. (She chose to live in denial.). She told my ex I’d written her. He must have thought I’d also told my son, so he told him a sanitized and minimized version of the truth. My son and I have talked several times, and I’m glad he now knows. Honesty enables trust.

Because your son is now an adult and seems to think you are at fault for divorcing, and you are still carrying the burden of your ex’s secret, which includes the quality of that relationship with your son, I would tell your son, sooner rather than later.he’s entitled to know now, and if you wait he may wonder why. (The only caveat to this advice is whether your ex would retaliate by withholding college money, although if his contribution is specified in the decree you could take him to court to honor it).

You can put it to your son that now that he’s 18, he is entitled as an adult to know the truth. I would not bring up his disparaging remarks to you. Just give him the facts. And if the divorce decree includes the reason for the divorce and the non disclosure clause, I’d show him that, too. Present it as your wish to honor his adult stays and in the name of an honest relationship.

OK, I did it!
I just finished having the big conversation with my son and it went well.
He actually started big belly laughing and said that was not the reason for our divorce that he was expecting.

We talked for about an hour and it seemed like a lot fell in to place for him. He showed empathy towards me and what I went through giving me lots of hugs and telling me he was sorry I had to carry my story for so long. He also seemed empathetic towards my Ex but could also understand how absent his dad was in both of our lives leading up to the separation. 

He said it will be awkward facing his dad the next time they hang out but he'll deal with it and has friends he can talk to about it if he feels the need. 

*phew*
Grateful for such a good kid. I feel the weight lifting
Thanks to everyone who chimed in; it helped tons!

yes, well done - so glad it went well Broom.