Hey! Sorry to hear what's happened. As one who's been there many years ago I just wanna say "good luck". My ex-wife did a runner with my young son many years ago, but she brought him back to me not long later (her new guy wanted his own family) & then cut all ties with him. She's missed his 18th, his 21st & his graduaution. 18 years later & he's never heard a word from her.
This has brought us incredibly close, so much so that many of his college pals thought "I was the coolest Dad ever"
, He's now grown up and we're still best buds as well as father & son & like has already been said, "he knows who's been there for him all his life". I'm not saying your ex will do the same, but your sons will remember how you've been their rock.
I'll be going to see him next week for a few days, just the two of us for a few "boy's nights out", without partners. There's a bar in Edinburgh with 28 bourbons, we've always reckoned we'll drink our way across it, never managed it yet, because we always settle on Buffalo Trace.
Cheers to you my friend, I know you'll do the right thing. You have all of our support & you know where we are whenever you need us.