I've messed up 4 people's lives & very confused!

Hi I need some serious advice!
I'm married with 1 child, my husband is a really great guy but just over a year ago I met a woman. I've always been interested, had a few encounters but this was different.
She still hasn't had any children but is newly married- 2 years.
We got together quite quickly & fell in love.
We spent so much time together but didn't trust each other initially(her being my boss at work!)
To cut a long story..just before Xmas her husband found messages on her phone bug her had suspected for a while.
They had a really rough Xmas but she convinced him to let her still see me & spend nights (although rare) with me.
Anyway we argued constantly, I wasn't particularly nice in the things of say about him and their marriage. It was always on her terms, of course she says she loved me, that I was better in every way blah blah...but my confidence was shattered because of how inconsistent she was.
We're a over a year down the line and everything changed- she now loved him more than me, sex was better with him, would rather spend time with him. She'd say anything for a reaction. The next day it would change to how great I was?!
So I snapped, I did something terrible. I sent him a letter telling him everything. Told him all the personal things we'd done, how inadequate she said he was. The things we'd done together, things that they do on special occasions.
It was awful.
So he read it..
The next day she still answered the phone reluctantly. We cried a lot, she said it was over, that she missed me, will always love me.
Even though I knew it should be over after what I did I couldn't let her go.
She wasn't horrible & neither did she retaliate by telling my husband.
We're all hurting and I'm struggling at home. But for me to do what I did, she's agreed I was heartbroken before I did it.
I don't want her to leave, I really am struggling without her, she was the closets person to me & she still says the same.
Last night her & her husband had a chat, she cried said she missed me & told him how she felt for me.
They're sticking together through it but I'm out of the picture.
I think I wanted their marriage to break up- very honest of me, very horrible really.
But I've never understood how she could be in love with 2 people like she kept telling me.
Ok I love my husband but I'm not in love, I'm in love with her.
She's still accepting my calls, not many of them though.
She's not texting at all.
The other day I went to see her, she hugged me, kissed me & told me that she loved me.
Confusing eh!
I would have changed my life for her.
She's obviously not prepared to do that for me.
Do I move on or fight for her?
I know her feelings are real for me.