Sorry to hear you're going through all that...one year is a very long time.
I have been where you are, I separated from my sons father in February after 10years and I thought that I would never get over it, but someone else came along 3 months later when I least expected or wanted it and I haven't looked back.
The only person holding you back from moving forward is yourself and by what you said your ex has clearly moved on.
I always believed there is someone for all of us out there and we just never know when or where we will meet that person...we just know when it happens cos that person will feel the same way too and nothing will stop you from being together.
I know it's hard and you feel you can't carry on but the best thing to do is pick yourself up, dust yourself off, hold your head high and embrace life and it's challenges.
That's what I did and that's what I made myself believe. I had to start over with a 5year old boy...I'm loving life now and have a great man in my life who came into my life at the time I needed it but didn't realise it.
Sorry for long essay, but hope it helps x