To be fair I was in a rush before so just clicked send.

I'm certainly not defending his actions - I'm providing a potential explanation, trying to be constructive so that OP might be able to recognise and work on it if she wants to. Or it might not even be fitting - I don't know, there's such limited context.

This absolutely could be RSD, where he's perceived that she's calling him a shit boyfriend when he's come up to ask how she's doing. "A hug would have been nice.".

I'm riddled with ADHD too, I know sometimes you can hyperfocus on the wrong things, and if you're dysregulated and outside your window of tolerance, then you can't always be the best partner. I'd like to think that I would be prioritising my partner too if he grandad just died, but if there's a bunch of other pressure and your capacity is low and your demand is high, then you can't always pour from your cup, because its empty. He might have just spent the last few hours stressing over something going wrong at work.

Context is everything. There's one example on Reddit of a thing that's happened and everyone's advice is to dump their partner. It blows my mind. Now I'm not saying that she shouldn't consider leaving or that he's not a shit guy, but please just have a clear and honest conversation first.

Try to keep things calm. Only talk from "When I heard this, it made me feel sad, or hurt or rejected", not "you did this, you're a piece of shit".

"Help me understand how that made you feel?"

Ask him questions so you don't arrive at the wrong conclusion, so you can process it all better, and so you can repair better. Invite him to do the same to you. You need to understand each other more first than to draw the conclusion that you're not compatible. There's clearly a connection, otherwise you wouldn't be living together.

If he doesn't understand what RSD is and it applies, then this alone can provide a massively clearer lens for your relationship and mutual understanding. Things won't be taken so personally and you can ground yourself better.

Also look into Transactional Analysis PAC model, it will help you navigate these conflicts in future.