I just have to say I hate the phrase "get over it". It seems so brutal, as if being hurt or made vulnerable by things that happen to you is something that shouldn't happen. It also feels like someone things the "get over it fairy" will show up and poof! You're over it!
I much prefer.. working through it. That can happen in a variety of ways and everybody will find ways that work best for them. It can be talking to a counselor, doing some reading, journaling, lots and LOTS of self care, and learning to be gentle with yourself.
Being honest with the couple that there are a few things you are working through from the past relationship is important, too, so that if something comes up that's really a vestige of that past relationship, you can let them know and they won't think it's about them. And maybe they can offer support in those instances, too.
I doubly second listening to Brene Brown. She has a couple of longer talks on You Tube, and seriously... awesome and wonderful.