Dazed and confused

I apologize in advance for this being so long, but I could really use some advice and wanted to represent the situation as accurately as possible.

Quick background on the relationship
- Together for 17 years, married for 16
- Married when I was 19. She was 24 and six months pregnant with our oldest son
- We have 3 boys ages 15, 12, and 7
- We’ve always been best friends and almost never fight, like literally 6 times in our entire 17 years together
- We’ve been through some trying times, especially the early years when we were both working and I was still in school, but I have never questioned the strength of our relationship or the love that we feel for each other
- I have a fantastic career and have enjoyed great professional success
- When our second child was born she quit work and became a full time mom
- We’ve had some ups and downs when it comes to physical intimacy, but never anything dramatic. I’ve always believed that our libidos are just on different settings and over the years I have grown to accept that
- Never any infidelity on either of our parts

Four weeks ago, two weeks before our 16th anniversary, I noticed my wife acting a little quieter than usual one morning and asked her if everything was okay. She said everything was fine and we pretty much left it at that until later that night she asked me if I wanted to go out on the back porch and talk. That’s when the rug got pulled from underneath me and I feel like I've been free falling ever since.

She told me she wasn't feeling connected to me and that the “spark” seems to be missing. She said that she started to make plans for us to go on a vacation but stopped because she couldn't think of anywhere we could go or anything we could do that would actually be fun. She said that when she thought about the future she couldn't stand the thought of living the same life we have now and having this same type of relationship for another 16 years. She said that she is often relieved on the nights when I am out with friends or doing my own thing because she can spend time by herself without me around. I was floored.

Before this conversation occurred I would have told you that our marriage was stronger than it has ever been, and I was the happiest I've ever been in my life. Sure, we are both busy with work and kids and our own interests (she plays tennis and I play golf and poker), but we still spend time together and would go out together once or twice a month.
Something you should know is that I have always been the romantic in our relationship. I will do things like write letters and give her cards on random occasions, and send her text messages while I’m at work just to let her know I love her and that she is on my mind. That has never been her nature and while I do crave that kind of expression in return I understand that’s not who she is and accept that she shows me her true feelings in other ways.

Ever since that night it's like I'm living with a stranger. She hasn't told me she loves me and I fear that's because she believes she doesn't anymore. We've had almost zero physical contact. She's told me that she needs some space and time so that she can work out her feelings and that I need to be patient with her. She hasn't approached me to talk about it again and I'm not going to try and make her. I know I can't force things or look desperate, but the truth is I’m barely making it through each day. The sadness, anger, and confusion I am constantly feeling has become overwhelming. I can’t sleep, I can’t concentrate at work, and I have that hollow pit feeling in my gut all the time and feel like I might scream out loud or break down in tears at any moment.

I'm going to the gym everyday and making it a point to spend time with friends and keep busy. In the end though I just want my wife back and what we had...