Most Helpful Guy
I'm sorry to hear this. Distance always adds an extra element of pressure.
I'm kinda old-fashioned with this, and I've always believed in doing this face-to-face... and be honest and straight up. Text or social media is a very impersonal way of doing this and leads to a lot of potential upset and misinterpretation from both sides. Calls aren't ideal unless you think serious drama might occur face-to-face.
Somewhere that's neutral, preferably not too isolated but somewhere you can both talk for as long as it takes without interruptions. If it helps, and you think you might struggle to get the words out, perhaps write down your thoughts in a letter and allow him to read it whilst you're there, and then ask any questions. This is how you learn from situations like this.
Most of all, stick to your guns, and be honest - really you've only got yourself to answer to in the long run, and although it sucks to do, you'll know you've done the right thing.