The fact he has gone to such lengths to hide it all from me just makes me think he still has feelings for her
I don't think there is any other realistic conclusion you can draw. Particularly as it's important to him to do it again.,and the lengths he went to to make sure you didn't know and wouldn't come.
I suspect he's still in love with her and never got past her dumping him. As said, I had a boyrfriend who did this to me and my father, it went on for five years, from 16 to 21, he was three years older, so 19 to 24, until my father took him aside and said "look son, this has to stop now, she's never going to go out with you again," . That's wasn't for my sake, it was simply my dad was fed up with him coming round to spend the evening with him, although he felt he was a nice lad. The age difference made it weird and my dad knew the score. He said he felt awful doing it, but it had to be done.
He seemed to be under the impression that if he hung in there, was in my family home, at some point I'd go out with him again. It's probably why I'm so invested in this thread, I've been the female on the other side.
I , for my part, didn't pay it much attention, he'd come round when I was home, and say " but you can't be going out" and I'd be like, yeah I am,,and he's still be there when I got back,, I'd just go to bed.
But he did have girlfriends and I always felt pity for them. I recall going into a local bar, and he was on a date, and followed me into thr ladies and asked me to go out with him. Just left his date sitting there, watching him walking into the ladies. I can even remember the look on her face as we made eye contact when I came out the loo.
What is weird for me though, is he was in a relationship with a girl who he dumped to go out with me. He is now married to her. He treated her appallingly over the following years, but she just hung on in there. I can't even imagine how shit that must feel. To be in love with someone who is in love with someone else.
As said, it's probably why I'm so invested in this one and urging you strongly to take a very very big step back here, because there is too big a chance this is going to end up killing your self esteem