I’ve not voted as I do think if you’re a couple then it’s important to be open about masturbation and things.
There's a difference between open and then being intrusive and behaving like you have a right to know everything about someone's private moments and not respecting their boundaries and OPs dh seems to fall into the latter.
I had a boyfriend who did the grabbing thing and would pretend he didn't know I was being serious telling him to stop, eveb with me telling him when I say stop or no, it means stop or no and he'd "forget" and just do it again next time.
He'd do the same for sex, especially if I laid away from him, he'd grind into my back, be told to stop because I have an early morning and am going to sleep and then five minds later he'd be trying to "tickle" my pubic area and get huffy and shitty if I moved his hand because he found the stroking my pubic area "relaxing".
He ask me masturbation questions like this and it felt very intrusive, he'd ask at weird times like when I was reading a book, or washing up, I'd answer some of his questions because when I'd said I'd rather not he said "good" relationships are fully open about this stuff and share what they think about, and he'd even said the fact I was so hesitant to tell him what I thought about during masturbations makes him think I was fa at asking about real life men or "had something to hide" He hated the thought of me using a vibrator without him too.
This is a made up example, but let's say I'd said my fantasy was with a waiter in an empty restaurant, if I so much as smiled at a waiter on a meal out he'd get very annoyed and ask if I'm sat there getting wet thinking about said waiter fucking my brains out. That type of stuff. He had this weird idea of "saving" my orgasms for him and if I masturbate when he was away then I'd not enjoy sex as much when he came back home.
I've been married over 20 years now to a totally different type of man and have never had my husband behave like he has some kind of right to know my private thoughts, we can talk about masturbation in a respectful way and if I'd said I don't want to talk about that then he respects that. When I say "I don't like being pinned down or jumped on" he doesn't forget and keep going when he's been asked to stop. I also don't have him asking if I'm getting wet watching a neighbours house burn down because I've said I like a fireman's uniform.