Well, I have left my husband in the past for issues  concerning SD, but I wouldn't leave him for this.

Now, I'm just going off the assumption that this is a knee-jerk emotional reaction to seeing your hubby having an enjoyable evening without you in pictures and not pictures of him getting it on in the closet with his ex-wife. *shok* Your husband was obviously there to support his son's achievement, regardless of who paid to help him reach that goal, and he should've been. 

I think, and I've definitely been there, that this is related, in no small part, to only being partially disengaged from your SS. It's obvious, from your previous post, that you have resentment toward each other, yet you continue to have expectations of one another. He expects you to continue forking over the money, and you expect to get an invitation to the event that would've never been possible if you hadn't been forking over the money. 

My suggestion is that you fully disengage. It removes expectations completely,  and will keep YOUR money in YOUR pocket. Disengagement isn't always an easy road because DH is going to still see his child, do things with his child, talk to his child on the phone, attend milestones and parties for his child,  and you won't be there to enjoy it with him because you are disengaged. Disengagement creates a lot of lonely nights and days, at first, until you get over the resentment and anger that DH left you and is having a fabulous time without you. Then,  you begin to realize all the wonderful opportunities you have to enjoy life, on your own, without DH and that not being subjected to the stress of those situations is divine!

Since your SS has extended an olive branch in the form of the letter you previously posted,  you might consider taking him up on the offer and arrange for a mediator if you're interested in attempting a reconciliation. You should also bear in mind that this attempted reconciliation might only be a money grab on his part so that you can fund the next graduation he spoke about. 

Whatever you decide, best of luck. 

The short of it is: Let the vipers lie in the viper's den, while you are at the spa or daydreaming or wherever you'd rather be. Vipers have no problem lying in wait with their own, and then once anything foreign comes across their path, they strike. 

You don't need to explain anything to vipers nor seek out their opinion. Like most vipers, they lack empathy. Just recognize them for what they are and avoid them. Your DH has long since learned how to deal with them or sneak around them. If he isn't going to carry you across the viper den, then the problem is his alone to bear. He knows how to take their strikes; you don't. Don't feel jealous at all about the graduation/ viper party. Like most vipers, for days they'll just be striking at others and showing their fangs all the live long day, and at the same time, going on and on about how much fun they are having (maybe?, but no one else is!!). You are MUCH better off at the spa or being home alone reading or painting your toe nails or whatever vs. being at that "event."

Painful situation, even more so knowing it's a sick game where BM & SS actually enjoy being sh*tty and aim to hurt you. Nobody deserves that, especially not a step mom who provided the means for that education. 

Hopefully knowing you have an anonymous online group of sympathizers who understand, who listen, and who encourage you, helps you get through this. We care, and we also understand what it's like to be on the receiving end of the needless insanity or behaviors, lies, and insults we did not teach & cannot control. Hope it's helping you to write it out.

Is he deliberately trying to wind you up? 

I'm totally disengaged from my partners Son so when graduation day came I didn't get nor expect an invite. 

She didn't make a song and dance about the affair, I mean why would you, people are rolling out of university like a sausage machine  it's no big deal. 

He is purposely trying to get under your skin.

Just out of curiosity, why did you put so much money towards this asshole?

He is trolling for grad gifts (MONEY!!!) from the only people, other than  you,  in his world with money... YOUR FRIENDS!!!

Write this pathetic shallow and polluted gene pool off and move on. 

I had a series of rescue projects over the years. Absolutely beautiful women each with a tragic flaw that I just knew I could fix.  Nope.  I can't fix anyone... or rescue anyone... without ruining my own life.  Not happenin. 

When my amazing bride invaded my life, as a single 18yo teen mom with a 15mo little boy... there was no rescuing her/them. I just had to stay out of the way and share life with this amazing, brilliant, scary/wicked smart, stunningly beautiful force of female nature. 

If you go, don't ever start another rescue project.  Make a life with someone who seasons your life and do great things together.

Good luck and take care of  you.

Pink, back when you had a big blow out with your H and your dad came to visit, I hoped you would file for divorce. You are being used as a sugar momma, and have been for some time. Why do you stay with this man who allows his son to mistreat you? Why?? Who's taking care of you? Who's planning for your future?

Now that Preshus has graduated, the gravy train needs to be stopped. There's absolutely no reason for you to ever give this entitled man another penny. Please separate your finances and hold your H accountable for half of the household bills and all the debt he's accrued.  If you must stay with him, then at least stop funding your mistreatment.