Welcome mama...you've obviously found yourself in the right place where people who know what you are going through can actually help you!
You are in a tough position, because the naturally LD person will almost ALWAYS become defensive when they are called to the carpet about being LD. Even though he has said in the past that it will get better, and even though he intellectually knows that you need it more often than once per month, he will still be defensive when you finally bring it up again.
To me, the best way to handle that is this: no matter how defensive he gets, you just watch him and realize this is how MOST naturally LD people behave and react, and you realize that his words are not a true reflection of how he feels. They are just the first REACTION to your bringing it up...but they are only in reaction. His words during that time are not his well thought out words of truth. They are just the normal defense an LD person puts up when the get called out.
You can expect this defensiveness in nearly every conversation you ever have with him....UNTIL one day you have the conversation that actually makes him want to do his part of the work. Until that conversation happens, he will be defensive every time. Just don't react to his defensive reaction! That is always your best tactic. Stay calm and loving, no matter what he says. (I do realize this is hard to do when you are sexually frustrated!)
For some people, that one conversation that actually begins true change, is an ultimatum, or a threat of a future ultimatum. For other people, that one conversation will happen in therapy with a counselor. And for still others, the one conversation will happen after the LD person reads the right book or article that really makes them finally "see" what they are doing to their spouse.
Always keep remembering that the naturally LD person really has no idea how sexually frustrated you are. They are not doing this to you on purpose to torture you, although it may feel that way.
Now I have to say one more thing, and this may not be a popular opinion...but if he has porn on his computer (or you have caught it in the past) then if I were you, I would simply demand that this stop and I mean NOW. I would also demand transparency on this issue (ie: if he looks at it, he has to admit it to you and show you what he was looking at). I would demand that from him because if he is wasting his sexual energy on masterbation while you are trying to recover an SSM, it will very greatly inhibit his desire to actually have sex. (And I also have the personal opinion that men are lazy lovers when they only masterbate to porn instead of using their minds and imagination...it is very easy to become visually aroused for them...the problem is that then their bodies associate ONLY visual arousal with sexual release...they begin to lose the association of BEING WITH THEIR WOMAN with sexual release...but again, this is not a popular opinion).
That's my two cents. Really happy you have found your way here! There is not too many other places like it!