@Pinkdelight3
Definitely move on. You've not missed out - you didn't want him, and the "I've known him twice as long", however jokey, shows the intense feelings are really more about marking your territory, wanting him to still be into you rather than you being suddenly into him after all this time. Be glad that he's found someone who likes him, leave them to it as much as possible, and look elsewhere for someone you're genuinely into. You sound like you know this really, objectively, so should be able to step back and observe and manage the feelings however intense. The 'caught' makes it sound like you have no control, but you absolutely do. Remind yourself he's not actually your cup of tea and don't feed into fantasies that he's anything other than the guy you didn't want to be with.
This is well said and the crux of the matter.
Remember, if he really was the love of your life, you would have realised it a lot sooner. And not just now when he isn't available to give you the attention you're used to. I'm sure if you had/or do meet someone else, you absolutely won't be thinking about him this way. But an idle, lonely mind has a tendency to cling on to happier times when you were less lonely and always had him as a back up.
Now that you can see it this way, take space. Do not meet up with him and his gf because (a) it will be torture for you, so don't do that to yourself (b) his gf may be able to pick up on the fact your feelings for him aren't wholely platonic, and he could stop the friendship completely out of respect for her. So leave them to it and focus on your own dating life, and finding someone of your own.
The most important thing to help you move on is to accept - that he has emotionally moved on from the crush. So while you may have known him longer, the intimacy and closeness they share will always trump what he had with you by way of a friendship. She will know all those little details, habits and quirks only someone you share a bed and a life with will know. Let him go, put in distance to help you move on, stop living in the past, and look to the future for happiness.