Confessions: I've cheated on my absent partner - should I confess?

I have been with my boyfriend for five years now, but over the past year he has been away overseas studying, which has been very difficult for both of us.

A few months ago, I cheated on him and can’t bring myself to tell him.
I've cheated on my absent partner
Every time we’re together, things are great, but when he’s away it’s almost like I forget I have a boyfriend.

What should I do? Should I confess?

He’s a huge part of my life – it’s hard to imagine him not being in it.