How to get over someone you never dated

Hi!
So my problem might sound stupid but has actually been bothering me for about 2 years and a half now.
I met this guy, lets call him John, some years ago while he was vacationing in my city. We kissed and met the following day were we came back to his place and made out there.
When John left, we kept texting for months and I thought something could be born out of just a simply hook up. I didn't want a relationship with him but I definitely thought we could meet again.
John and I stopped talking, I moved to Europe and I met someone else who really liked me and who I really liked too. I started dating this new guy and we are currently on our second year of relationship. The problem is that in all this time, I haven't forgotten John and I constantly think about him. My boyfriend lives in the same city than he does which doesn't help either.

I have a friend who happens to work at the office where John works. Should I show up to casually run into him? Is it dangerous territory? I love my boyfriend and he loves me, is it worth putting at risk our relationship? How do I stop obsessing about John?

HELP!

Thank you :)