Oh, my goodness. What? “I almost feel like being mocked when he’s asking “what are you doing today?” Am I wrong?” Yes, you’re wrong.
And what’s up with this: “If I were not in committed relationship with him, I’d see other people, and probably would have made plans, most likely.” You knew well in advance your SO wasn’t going to spend the day with you – so your “committed relationship” excuse doesn’t fly. You set a trap for your SO and it backfired.
You’re too old to be playing games like this. If you wanted to spend the day together, you should have said so. If he couldn’t because of that specific situation – his kids and family – then you could have set up alternate plans. Instead, you did nothing and now want to blame him because it felt shitty doing nothing on Thanksgiving, even though you knew full well he wouldn’t be able to be with you on that day and you deliberately chose to not make other plans.
Next time, take control of your own holiday. Playing childish and stupid games leads to winning childish and stupid prizes.