I saw my boyfriend's phone and now I can't sleep

My boyfriend of 2 years left his phone on the bed when he went to shower. I wasn't even planning to look. But the screen lit up and I saw a message from a girl saved as 'Babe'. I opened it. The message said 'I miss you, when are you coming back to Abuja?'

I scrolled up. They've been talking for 6 months. He calls her his girlfriend. He told her he's single. I sat there with the phone in my hand and my whole body was shaking. He came out of the bathroom and saw my face. He didn't even deny it. He just said 'Chi-Chi, it's not what you think.'

I packed my things that night. But the thing that's killing me is that I keep wanting to call him. I keep thinking maybe I overreacted. Maybe he'll change. It's been 3 weeks and I still check his WhatsApp status like a fool. Why is leaving so hard when you know you're right?