Hi there..
For the letter talking about how genuine your relationship towards your partner is that you're going to wrote a letter that says your love and relatioship to your husband is truly genuine. You ca say anything how u felt towards your relationship.
On our case we just make a letter address to the CEM and we talked about how we meet , our plans together in the future. It may sounds so gay or corny to say how you loved your significant other but thats how they will see how truly genuine your relationship is.
Goodluck to that!