This has happened to me. I think that you’re doing the same thing I did and are placing Ted up on the “OMG perfect guy one who got away” pedestal. But to be honest a lot of things you e said indicate to me that he’s imperfect in important ways.
Some people really like attention, and for some straight men, attention from the opposite sex is the best. He clearly loved the attention you gave him and felt some sort of way about you, enough that he really cared about you deeply as a friend, to engage with you probably knowing you had a thing for him.
The fact that you kept resuming a friendship after things went down demonstrates that this guy clearly has a boundaries problem. I imagine he is like this in any relationship — and if you were to somehow be with him, he’d be doing something as confusing with someone else outside of your relationship. Not that it’s the worst thing you can do in the world (although I do think leading someone on — and he was, you felt led on, his gf felt he was leading you on—is a cruel thing to do). It does mean this guy likely has some unresolved issues with regard to attention or what he thinks vs what he wants, and that will be a long road for him if he continues on the way he is.
The good news is, his problem is not yours. And I found the best way to get over the guy I had feelings for was to focus on work and eliminate all interaction with him. I think it’s important you draw a boundary with this guy where you no longer are friendly to one another. Awkward sure but you need to being self-preservation mode. Not only will limiting contact quickly make you feel better, but being the one to make that decision and initiate a withdrawal from him with make you feel in control of the situation.
And really, remember that this guy slept with you, went home and probably freaked out because he crossed the line with someone he works with and was already kinda dating someone, but then proceeded to develop a close friendship with you anyway. His words don’t match his actions and that is really unfair and indicative of a larger problem — for him.