Why is it so hard to leave

We broken up on the 7th November and since then I returned back to our home to work until my new job starts. I’ve been here for 14 days and tonight is the hardest night as I’m having to leave for a couple of days. I found myself watching him playing with our puppy dog and I couldn’t help but have tears in my eyes. I said please make sure you play with him. He said your saying it as your not coming back in a couple of days, I said I am but in that moment I had taken myself out to the bathroom and just broken down crying. It’s becoming more harder to keep saying goodbye.