I think loads of stuff has been covered well here by PPs - he's being a dick, he's being insensitive, and generally he needs a proper talking to about how this made you feel.
I wanted to add something though - absolutely not in his defence, because his behaviour isn't acceptable, but to maybe explain why he is this way about sex. Because I was (in a much less dickish way, I hope) the same for a long time and it's something I still occasionally remind myself of.
I like sex, and it is a non-negotiable part of a relationship for me. Not non-negotiable like, when I want it goes, but as in, 'would not have a romantic relationship that didn't involve sex at least semi-regularly', and in that it doesn't really matter to me what external pressures I'm under or if I'm ill or whatever - my base level of desire doesn't change. My partner (and some other partners in the past) aren't that way: it's a 'nice to have', or they're much more likely to have their sex drive wax and wane based on what's happening around them.
Because I was coming at it from a 'this is a key part of our relationship and needed for connection' and they weren't (or weren't always), when we didn't have sex for a while I would find myself frustrated and hurt and rejected. I didn't understand why they didn't want to do this thing that was part of our relationship - it would have been like stopping talking to me all of a sudden for weeks, for example. Now, I kept that to myself, but if it ever came to a head and I needed to talk about why, they'd be saying "Oh, I've not been in the mood" and I would be interpreting it as "I am not in the mood for our relationship, you by extension, and by expressing care and affection for you.". That made me unhappy and short in the same way that being told ...I dunno, he thought I was annoying would. Eventually, a very understanding and kind ex of mine explained that actually, how I saw sex wasn't how he did, and that while I'd be happy to have sex right after an argument, with a horrible headache, during a stressful time at work, that he didn't, and that it wasn't a reflection of how he felt about me overall, but how he felt in that moment (or, obviously, if we'd argued, also about me). I learned my lesson and learned to stop treating the frequency of our sex life as directly analogous to the health of our relationship overall (obviously, sometimes they are linked, but not always).
It sounds so selfish and short-sighted, granted. But I was genuinely hurt and rejected by the fact that he was - in my eyes - rejecting me and 'us'.
Your comment where DH said the comment about your uncle being a 'low blow' is what sparked me to write this - he was treating that as an argument, where one might make a 'low blow'. And that made me think that he too might be seeing the function of sex, or its importance, or the consistency of his libido in a different way than you and - clearly - seeing your 'refusal' (which is absolutely, 100% your right) as you rejecting him. If I picture myself in this exact scenario, where I'm your husband, I can see myself feeling frustrated and confused about why wouldn't you want to have sex when you feel shitty and something bad has happened, it makes you feel better? Wrong (for lots of people, anyway), but true for me, if not shortsighted.
Now, he's still been a twat. As I was. And he needs to learn, as I did, that not everyone sees sex like that, and he needs to apologise for how he's behaved and for not being appropriately supportive.
He might not feel like I did at all, and he might just be an enormously selfish dickhead - only you can really judge that, I think.
But I just wanted to offer a possible explanation. And, I'll add again, because I really, really don't want to be seen as excusing his behaviour - he is most definitely in the wrong. It just might not be coming purely from a deliberately selfish place.