mssalty,
First . I'm sorry that you're going through this, and I understand some of what you're going through because of my own situation. My ex quickly shot down, argued with or demeaned everything he originally said he loved me for. All of a sudden I wasn't able to be me, and I fought against it most of them time, but some times I couldn't anymore. He's been gone for five months now, wants a divorce and has already moved on to someone new though he lied about doing so.
It's taken me a long time and a lot of help, and I still have a long ways to go, but here is some of the things I've learned that I hope can help you in rediscovering you and being able to be ok with you whether anyone else is or not.
First, baby steps. I wanted to leap ahead and it put me back, so remember to take it slow. It took you some time to get to this place and it will take you some time to get back. Start with little things like asking yourself questions. Do you love yourself the way you are now? If not, why? If you don't feel like you can be yourself with your SO, then what relationship can you truly have together? My ex never took the time in eight years to get to know me. It all vanished after he married me and grew worse over the years. These last two years I've worked hard on trying to find me within the relationship and it hasn't been easy, but it's possible.
I can sometimes remember clearly who I was, and sometimes it's all murky. Look at pictures of yourself before being with your SO and specifically look at your eyes. Mine were so alive and clear. Right after he left, they were almost dead and I didn't see the difference until I happened upon an old pic I took while looking at my son's photos. I cried for her, for myself. It shows on people who have been worn down and I'm sure you'll see it.
Don't try to change everything all at once or you'll set yourself back. Just, if you can, take each baby step with determination that you can do this. If, little by little you change and your SO sees and actually appreciates and changes too, that's great. If not, that's when you'll have to make a decision. But, for now, try to work on accepting and believing that you are the person that you felt for those few beautiful days.
I don't know you personally, but I feel for you as though I do. It's painful living that life and it's painful trying to heal from that life. Nothing I've said is a mandate, just my personal experience. I'm sure others will have better advice, but I wanted you to know that you're not alone and you don't have to miss yourself, you can be yourself.

Purekalm