I will get flamed for this - was on the other thread and have NC's for this as it is not very MN advice. However - what it is is my real life experience and something I have talked about at length to a number of real life friends..
Just do it. I have a DH with a high sex drive, we probably have sex 3/4 times a week. I'm not really that fussed. It is quite rubbish and quick a lot of the time, sometimes it is better than that. If it was down to me it might be once a month, or less.
It is genuinely how people get along in real life with their partners not looking elsewhere, especially if everything else is alright. I honestly don't get this idea that all of these people in long term relationships are burning with desire and horny and desperate for a shag with their DH's and that is when sex will happen and only then, that is bullshit, and an entirely unrealistic expectation which puts a lot of pressure on people who think that this is a reality. Like it is not reality like porn isn't reality, or romantic films are not reality. It isn't real.
I do not believe that everyone is up for it all the time at the same time as their partners - a lot of people, when propositioned for sex by their partner when they aren't feeling it will (in their heads) will be thinking 'oh for fucks sake, go on then' a lot of the time. Doing it to keep their partners happy. It is JUST sex, it isn't torturing small animals or poking yourself in the eye or sticking a poker up your arse. It is just plain old sex, just do it, then he/she is happy, you move on with your day, no fuss no drama. If an entire generation goes along with this fantasy that you both must be in the mood or it doesn't happen that is bonkers. No wonder relationships are so short lived these days!
Anyway, rant over - the PC police will be along to tell you that he must respect your space (of course he should - not advocating anything else) and that you should only EVER do it when YOU want it and that's it (obviously you need to consent btw, that goes without saying, but IMO you can consent and be doing it, consensually for reasons other than being desperate to shag him/her. For example I will consent for an easier life, or because I love him and I want him to be happy and in a good mood. Or because, if I don't then eventually I will be bringing up our children on our own whilst he finds somebody else to have sex with).
But it would be really really interesting to know whether anyone with the opinion that only when you are well up for it should you consider it is honestly in a long term relationship with that attitude, low sex drive (but with someone with a higher sex drive), both happy, with a faithful partner who is willing to live like that forever?
Lastly your DH sounds lovely, and understanding and he may well be one of the good ones who will live like that & I am only saying what I have found to be true for myself and my friends. I hope you find a solution that works for you OP.