Hi esbest8,
I also encourage being open with him IF YOU CAN, so he will understand not to bother you for a bit to do the exercises. When I explained what vaginismus was to my partner in simple terms and casually (something like “involuntary closing/tightening of the muscles around the vagina, making penetration painful”) he was super understanding and when I explained the dilation exercises he also completely got it. Occasionally when I used to dilate daily, I’d even dilate under the blanket with him next to me (I’d usually have headphones in and be watching TV/Netflix on my phone).
Obviously everyone’s partners are different and people feel differently about being so open with their significant other, so I understand if you’d like to keep the dilation practice from him. In that case, trying it in the bathtub seems like a great idea. Or if you know he is busy for an hour or so (working from home or watching TV or something), say you’d like to relax in the bedroom and do it then.
Cheers and keep us updated!