When it goes around does it really come around?

Today I had lunch with my best friend whose name will be changed to...Darien. He and I met in high school and at first we both had the idea that we hated each other when in reality we didn't. We became friends during community college but it was mostly because we were in the same clubs; so in reality we knew each other because of high school and because we were in the same clubs. Then I transferred to a four year university, we kept in touch with the occasional phone call and or email then we lost contact for a while and then about two years I sent him an email and actually got a response from him, one that changed our friendship for the better. We went from supposedly "hating each other" to being acquainted to one another to becoming best friends. Funny how that happens but I will admit that I've had or rather still have a crush on him but I've gotten better at hiding it. Now I know what you're thinking... "why don't you just tell him?" Well I did about a year ago I finally told him I had feelings for him and his response was... well he's my best friend for a reason and basically it's because he didn't have the same feelings for me. Which is fine, I don't let my feelings for him stop me from seeing other people, I've gotten to gotten to know Darien very well and I have to admit it's nice to have a friend like him in my life. He's one of those friends that you know will be there when you need a shoulder to cry on or just to let you rant when needed, and I speak from experience on both of these accounts. He has let me cry on his shoulder on more than one occasion and the one thing I love about him is that he lets me cry and does not push me to stop. He is an amazing man and I love him very much for that. Now the reason why I am posting this question today, he told me a very interesting story, after I finally told him a secret I had been keeping he told me one he was keeping as well and no he does not have secret feelings for me on the contrary a girl he used to like years ago while we were at Community College, who in the end didn't not return the feelings at the time. Well apparently he didn't take the rejection very well for a while which I didn't know, but then he got over it and got over her. Well this year that same girl told him just recently that she has feelings for him. And like her years ago he does not see her that way. Now I know this girl and I know for a fact that she will get over it and will eventually move on; but here's what I found interesting years ago he told her he liked her and took her on a great date and after many years she would compare all of her dates to their date and in the end she developed feelings for him just to get rejected. So this is why I ask the old saying what goes around comes around, does that really happen? He liked her but she didn't like him and then many years later she realized he was a great catch and was an idiot for not taking the bait while she had the chance, she tries to reel him now but in the end gets rejected just like he did years ago. What do you think? When it comes to dating does it really come around or are just idiots for not seeing things sooner?