I’ve been friends with this individual since middle school and have now since been in college for a couple years, we’ll call my friend, S.
For most of high school and out I was in a relationship with a girl while S would date around and try things with different girls. We had an event happen with another friend in high school, we’ll call that friend H.
H was doing the long investment work with a girl, a girl that mostly “friend-zoned” H. H was absolutely all over this girl, and determined to win her over! It was well known to all of our friends. Well sometime after that H had plans with this girl and she totally bailed on him, to find out that she made plans with S. Few days after that we find out the two are now an item. In a sense S knowingly started romantic interests even though they knew H was interested. 
Well S did this not once, but TWICE to our friend H. 2 different girls, where H believed he had a shot and S swooped in and “Mister Steal Yo Girl’ed” him. The first time H accepted his apology and they made up after a snarky text, the second time H was mad at him for about 2 weeks and they got over it. 
Fast forward, outside of high school in college. S and I work for the same company but different locations. S is having a bday celebration at Buffalo Wild Wings. S’s long term work crush is going to be there, a girl who has placed S in the oh-so fabled “friend-zone”. You might see where this goes...
His crush and I hit it off, meetup a couple days later. We hookup, have a great time, and promise each other we won’t tell S. Well, I happened to have told that information to a mutual friend, which in hindsight I regret. That mutual friend of ours informs S. S completely cuts the girl out of his life saying “I’m only going to be professional at work and that’s it to her” after being friends for months. To me the last thing he said was “Fuck off you’re the last person I want to talk to” my response being “I’m ready to talk whenever you are.”

So am I the asshole for what I did? Do I owe my friend an apology or need to make it up to him?

TL;DR
Friend steals another friends crush 2x. Without the victim doing much in retaliation. I do it to that person and they completely cut me out of their life. 