But I do agree that reading stuff he's saying and doing does NOT help at ALL. If he seems happy, you're insulted and hurt. "How can he be ok without me?!" If he seems depressed and unhappy, you're confused. "Why did he leave me if he's not happy without me!?" You can't help but make every single thing about you, and it probably isn't. Also, it's not DIRECT words to YOU, so they can be misinterpreted very easily as sounding overly casual or flippant or careless when they're not meant to be.
In terms of your ex reaching out and saying happy holidays...this is hard. I would find that harder than anything else, personally, because it seems he has moved on if he's able to be friends like that and nothing more. It's so hard when all you need is for that person who used to love you above all others to understand how you feel and be there for you, and he's the one person who can't because he's moved on.