As I said before it's okay to do nice things, and be nice... in fact you may even like yourself better knowing you are nice!!!! I LOVE that you wrote that letter to your wife. Now, the trick is not to expect a darn thing from her. Just accept that she will do what she does because she can't yet appreciate what an amazing guy you are. Hopefully she'll wake up sooner than later to realize that. In the meantime work on continuing to be a great guy and don't worry about her words or reactions. Consider her hormonally challanged at this time in her life (and keep in mind most women are so if you can learn to detach and deal with the one you have now you'd probably be better prepared if things change in the future).
Another thing to keep in mind... sometimes it takes months (and even years ) to melt an iceberg. Sadly, it can be a very slow process. But don't consider it wasted time. Consider it an opportunity for you to work on being a better, more patient, more wonderful guy, dad, friend, etc... No matter where your marraige goes you are not losing anything if you are working on yourself, being a great husband (even if she doesn't appreciate it or realize that!) and enjoying your son.
Yes, weirdly, I am with my husband. He finally "woke up" and told me he wanted to stop the divorce. I didn't think we'd get back together because he's a pretty determined person who makes a decision and doesn't change his mind and he was CERTAIN he wanted to divorce me..... I chose the name Runningoutoftime because the divorce had been filed and I felt like I was on a time clock to get him to question his decision (that was my first goal!).
By the way, when I used to leave "extra cookies" or little notes thanking my husband for a bill he paid, or cleaning the pool, or whatever.... he would never acknowlege them. He held onto the anger and meanness as long as he could... but eventually my niceness did win him over. I think they don't trust it in the beginning. They think you're doing it to get something back.When you can do it without expecting anything.. well, that's a real gift.
It's kind of like when I sometimes buy coffee for the person behind me in line at the drivethru coffee place. I don't know them, they don't know me, I don't leave my name or expect anything in return. I'm just some stranger doing something unexpectly nice for someone else. It only costs me a couple dollars but maybe I've made someone's day a little nicer. Live like that....
There is no arriving, ever. It is all a continual becoming.