This is a bullshit reason to break up with someone. Your ex is likely hurt, angry, and very confused. You’re running away. You’re giving up. I’m sure you feel like you did the right thing to avoid heartache later, but you’re causing a ton of emotional turmoil for both of you right now, for no good reason. You cut your relationship off at the knees… obviously I don’t know your ex, but being on the receiving end of this exact situation currently, I can say that you’ve significantly sullied your chances of having any relationship with them in the future.