I hope this helps. What I think you should include in this letter is the pros and cons of your boyfriend. Except for the cons, you tackle it and change it into a problem that is solvable. For pros, he is someone that can support a family so in the future your mother won't be seeing your daughter in a poor status. For cons, you could say that, sure, he's got a big fat ego but it is something that you can change because since you control the situation in this story, you just state that you've been able to make him eat at stalls that rarely people with high status go to. If that's not strong enough, you could also state that at least he was able to go visit your mother at kampung which is a place that rarely people with high living standards go to. I hope this helps.