I know the holidays can be hard. Esp with all the nostalgia between sappy holiday movies and family gatherings, it's hard not to reminisce.
Do you have any time off over the holidays? Is there something you can do to keep you busy and not ruminating?
I am a pretty big advocate of social groups. I run a group on meetup.com and that helped me immensely through all this. The last thing you want to be is a ":)ebbie Downer" to strangers so you talk about things OTHER than your ex. If you have any groups in your area I really encourage you to check them out, it's free to join and there might be a trivia night or crafting event where you can meet some new people and have fun doing something.
I know what you mean about being well-educated and doing well. My ex was over 50K in debt with a gambling problem. I am pretty frugal and live below my means. This relationship ALMOST ruined me financially.
It's amazing how we become attracted and even addicted to a bad relationship with a person who is not at all like us, the opposite of everything we ever wanted.
I wanted to save mine and "saw the good" in her. I suspect that is what you did as well.
My best advise is try to get back to enjoying life without this person. I know you have to deal with him at work but if you can compartmentalize your interactions with him it will help. What I mean is, once your interactions are done for the day, clear your head and do something just for you, even if it's a walk to get your favorite ice cream or a trip to the gym to work out, maybe treat yourself to a massage afterwards.
Go to the cheap show and get yourself a small popcorn and treat yourself... .you don't have to share!

The hardest part when these relationships end is that the drama ends. I never considered myself a drama queen but I became addicted to the drama. I remember walking with my dog a year after the break up. It was fall and it was just us and the crunching leaves. Everything was calm, quiet.
I now enjoy the peace again. I mentioned in another post, having dated a BPD I realized I had also surrounded myself with unhealthy people. I let go of about 10 people this year who were psychologically/verbally abusive and can truly say I am happier. My ex's sister works with me and she along with my former best friend (who was a confidant during my relationship with my ex) have tried to ruin me at work. My ex BFF "un-closeted" me and has spread vicious rumors.
It sucks. It sucks being betrayed but you know what?
I don't react. I truly believe "loose lips sink ships". Both these people are viewed badly by management and colleagues. I am content and happy, I project that and it pisses them off more unfortunately... .
but I am going places. I carry myself with dignity and respect. Two things these people know nothing about.
Stacy, Meditate, reflect, but don't ruminate. You have so much good in your life and yes, your ex sees that.
Don't let him frazzle you. You have the potential to go far... .
he won't.
PW