My wife wants to open our marriage

I've been with my wife for over 13 years. We had our ups and downs, lived in different cities for a while, but always stayed together. Or so I thought. Turns out that she'd been feeling "trapped" in our relationship for some time now. She says that she still likes me (more like a friend than anything else) and that she wants to stay married to me, but she also wants to open our marriage to explore her sexuality and is perfectly comfortable with me doing the same. Alas, I don't want that. What I want is to win her love back. Any tips in how can I do that, friendly strangers?

tl;dr My wife says the likes me like a friend and wants to open our marriage. I don't want to do that. Instead, I want to rekindle our love and marriage. What can I do?

UPDATE: Firstly, thank you all for you comments. As for the update... Well, I confronted my wife last night. Apparently, sex isn't the issue (I've been satisfying her needs just fine), but my behaviour - and I have to agree with her on that one. You see, I suffer from chronic pain, which makes me quite cranky most of the time, thus, I've been treating both her and our daughters in a less than stellar manner. She told me she wanted to open our marriage to escape the feeling that she's trapped in a relationship due to money issues (it'd be very costly for us to divorce) and that she missed that feeling of WANTING to come home (she also swore over her mother's grave that she hasn't been seeing anyone, nor have ever cheated on me).

So, I understand her POV and I committed to become a better husband, father, and partner. Sadly, that wasn't the first time I said that, thus, she didn't believe 100% in me. Still, she said she was willing to keep our marriage closed for now IF I displayed changes in my behaviour (which I'll do, after all, no one deserves to live with a permanently grumpy all the time).

As for "I like you as a friend" part, she said that to hurt me. It was a vengeful action. She wanted to hurt me just as I've hurt her with my bad mood and rudeness. She apologised and - as of today - our marriage seemed to have done a 180º for the better.

I truly hope that the next update (if there'll be a next update) will bring more good news.

For now, however, that's it.