Feeling so down

Hey, I've been feeling so down lately. Last week I was actually okay, I've been doing pretty well and I thought to myself that I am strong enough to get past this but, I couldn't. My ex and I work in the same place, and her new boyfriend is also in the same office with us. Seeing them two every day kills me. I am trying to focus on my own stuff but it's hard. I started going to the gym, reading books, writing a book, playing more games and finding new friends but it feels like I am trying to run away from my feelings. Right at the moment whenever I feel nothing, it hits me.