I sometimes hear from folks who are so angry at their spouse that they are not even sure that they can address the problem face-to-face. Many are looking for pointers as to how to write a letter to get their point across because they do not trust themselves to state this verbally. They worry that if they try to tell their spouse that he is acting so selfishly and insensitive, a fight will ensue and things will only get worse. So a letter can seem very attractive when you are this angry.
A spouse might say: "Lately, I have noticed that almost every decision that my husband makes is selfish and based only on what he wants. We have been saving for a down payment on a house. My husband's friend recently had a financial crisis and he needed to sell his car. He offered my husband a very good deal on the car. And my husband bought it. The thing is, he didn't need a car. And there went the money for our down payment. He said that the car was too good a deal to pass up and that it would last him a long time so that he won't need another car. He said in the long term it will save us money. I do not buy this. He just wanted a nicer car. And now his selfishness will cost us time living in an apartment instead of a house. A couple of weeks ago, my husband got a bad cold. I took the day off of work to take care of him. But when I caught his cold and I was just as sick, do you think he tended to me? Of course not. There was no meal for me. There was no time off. He didn't seem to worry about what I needed. His worries are always for himself. I could come up with example after example of this type of behavior. Occasionally, he will surprise me and do something sweet or selfless, but this is very rare. Mostly he acts like a self-centered jerk. However, I hesitate to come right out and call him selfish. He won't take kindly to that. So I want to write him a letter. But what should the letter say?"
You're right to want to tread lightly here. Even though you may attempt to say this in as diplomatic a tone as possible, he can still read between the lines and see that you are calling him selfish and/or self-centered. And although you may feel very justified in this and you want him to know exactly how you feel, you have to ask yourself what you really want and what you are really trying to accomplish.
Act Only After You've Considered Your End Goal: Ultimately, you likely want him to act in a way that contributes to your meeting your long term goals - like buying your home. And you want him to act in a way that makes you feel valued, cared for, and loved. You have to remember this because if your strategy involves calling him out or making him feel selfish, then you are not going to be as likely to get what you want. Because he may feel defensive.
Even if you are successful in making him feel guilty, it helps to understand and remember that people tend to avoid and move away from things that make them feel negative emotions. Even if neither of you realizes it, he may well tune you out the second you start alluding to his selfishness - even in a letter. As soon as you start using the language where he can see where you're going, he's going to start skimming the letter so that he doesn't even fully appreciate what you are saying - much less take some action.
Catching Flies With Honey Instead Of Vinegar: I have found (and many wives agree) that the best way to get your husband to do something that isn't in his nature is to lure him into doing what you want and then praising him when he does it. You can do this in person or through a letter. But using positive feedback is so important. Why? Because in the same way that people shy away from negative emotions, they move closer to positive ones. You will be moving with the tide instead of against it. And getting what you want will not only be easier, but he will not be defensive or resisting you. (I learned this the hard way during my separation. More on that here.).
Look for an opportunity to ask him for unselfish behavior. Perhaps the next time you are sick, ask him to make you dinner. Or the next time one of you runs into unexpected money, ask him to set aside a separate bank account for your house. When he does those things or even takes baby steps, praise him. Tell him how cared for and safe it makes you feel when he makes these efforts.
Understand That Men Have Different Tendencies Than Women: I know that sometimes this seems unfair - as though you have to lure him to do something that is just basic. But being a caregiver isn't intuitive for many men. They grew up with mothers who took care of them and did the things that we are now expecting them to do. It doesn't always come naturally to them. But if you criticize, not only do they see you as the bad guy, they will often want to do the task even less than before.
But if you can make them feel like they are your ally and that you appreciate them, they will so often rise to the occasion in a way that makes everyone happy. You've said that your husband DOES exhibit unselfish behavior occasionally. This is important because it shows that this is in his character. He just needs to know that you'd like to see more of this and that there is positive reinforcement when he does.
I wish that I had realized some of this before my marriage started to decline. I used negative reinforcement during my separation and it was very costly. I had to change strategies, but it was almost too late to save my marriage. Almost, but not quite. You can read the whole story on my blog at http://isavedmymarriage.com
There are links to more articles about saving your marriage at http://isavedmymarriage.com