My ex partner recently left me for another woman when our baby was a few days old so I know how you feel and it’s utterly heart wrenching.
My advice would be to try not to go down the rabbit hole of knowing too much about her, keep yourself away and don’t hurt your heart deliberately by comparing yourself to her.
Reach out to old friends or those you’ve lost touch with a bit. I had so many people want to reach out to me when I went through it and it was honestly so nice - you can then arrange to meet up with them and have plans and distractions. Do not feel bad for leaning on friends and/or family - they want to be there for you and help.
Start a new hobby, meet new people and get out there. Do not get into the habit of staying home, not getting up, showered, makeup on and hair done - it makes the world of difference.
Set up an online dating profile, even if not seriously looking to get into something, it gives you people to chat to and a little attention so you can feel better about yourself and start to realise there’s a future for you once this pain begins to pass.
Take it a minute, an hour, a day at a time