You're right, it isn't fun when they don't enjoy it. That's where part of the excitement for me comes from.
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I think there is an important difference between not enjoying something vs finding something unpleasant. While I would want my partner to desire and enjoy what we do, I think it is fine some of the time to do things one does not enjoy. But one should not feel pressured into doing things they find unpleasant.
However, one's preconceptions (mis-perceptions?) can lead us to expect something to be unpleasant when in fact we won't. I remember as a young child my dad telling me about this candy which had peanut butter inside the chocolate. To my 5 yr old mind that sounded horrible. Fortunately I was brave enough to take a small taste under the encouragement of my dad.
There may be ways to introduce bondage subtley. For example, you could tell your husband you want him to use you as his sex toy. Tell him you want him to have fun and do whatever he wants tonight. (Reminds me of the meme of a wife in lingerie tied to the bed, the next panel is the husband at the shooting range. Caption: She told me to tie her up and do whatever I wanted ....).
Or you could be even more obscure. Tell him you want to try a new game. His Night - Her Night. Some of your sexual encounters will be designated as either His Night or Her Night. Alternate his - hers, with other nights just being whatever you normally do. On His Night, he gets to choose and set up whatever he wants. On Her Night, she does. You could add a rule that on His Night, she doesn't do anything without his direction. Don't kiss until he tells you to. Don't take off your clothes until he tells you to. If you approach this incrementally, you will get him desensitized to his preconception about bondage.
Introduce him to the Safe Word. Some word other than "No" or "Stop" which indicates the person wants the activity to stop there. The reason for using a different word is that you may want to playfully use "No" or "Stop" as part of your game.
There are a ton of sex games for sale. I have never seen one in real life, but perhaps a card or board game could be a safe introduction to a wider pallette of acts.
One additional thought. He may have some kind of trauma in his past or in the past of someone he knows. e.g. A friend who was raped as a teen, or a physically abusive relative who hit him. So he may have a strong reason not to go in this direction. If that is the case, he may not divulge it to you, and it may be a barrier you end up having to accept.