Simply replace the unfilled areas such as "" and "[date]" with your information.
Dear [name of spouse],
I know we have been going through some rough patches lately, and we've both been ill-tempered. There have been words on both sides that were hurtful, and we seem to be hitting issues that we can't handle on our own.
But we've been married for [years married] years, and I think that our marriage and our relationship is important enough for both of us to save.
I know that I would do anything to keep our marriage solid, and I would like to see a marriage counselor. I think that having the help of an objective third party may be just what we need to get past these issues and continue with our relationship.