If you are doing it the shidduch way than you would go through the shadchan which is a big part of making our life less complicated when things don’t work out. However if you dated a while and are/was emotionally invested I believe the right thing to do is speak to him directly (over the phone will probably be easier then face to face)
I was on the other side of your story. The guy called me to break it off and gave his reasons. I was terribly hurt but took it with grace and thanked Hashem for a while after (and still today) that it didn’t work out.
Comparing is a natural normal thing which can be good in helping you build a healthy relationship but can also be destructive. Because you dated this guy for a while you will definitely be doing a lot of comparing. If you give yourself time before you meet someone else the less likely the comparing will be destructive.
Good Luck!