New year sadness :( in Will I ever get over it?

I recently (within the past 4 months) broke up with my ex of 5 years. I was finally fed up with his constant cheating and lies, after finding out he had been sending multiple females money and going on dates with another. Initially after the break up I felt relieved and free, although I was hurt by the betrayal I still tried to focus on the fact that I was being strong by not putting up with disrespect. Immediately after he began dating the girl he was going on dates with, as of recently they have started posting couples YouTube videos and I couldn’t help but cry, because all I could think was “how does he deserve to be in a happy relationship with the girl he cheated on me with and i’m alone.” Yeah, I know I sound pretty pathetic, but I went through so much with him and all in hopes that he would one day change and be a great man and one day husband to me. Getting him to show affection, communicate and be faithful was like pulling teeth, but now with this new girl he has all of a sudden turned over a new leaf and is doing all of the things I needed from him for her. It’s a sad reality for this to be the outcome, but I’ll just have to pick myself up and move on. Maybe everything was for the best and she is the right one for him and eventually I’ll meet the one for me, but for now i’m just hoping this feeling of sadness will go away.