I've never shared this with him (he's very vanilla and this would probably shock him), but one of my favorite fantasies is a free use world, where I have to watch other women make my husband horny, and he's allowed to use them right in front of me.

Usually I'm looking on in jealousy while he's staring at a woman's large breasts. She's shoving them in his face and he can't help but touch, oblivious to me. She starts stroking him. Maybe a man comes up to me while I'm watching and grasps my breasts, testing them out to see if he's interested. I just let it happen, since I'm not allowed to stop any man who wants me. He slides his dick in as I watch the woman flirting with my husband take his cock in her mouth. My husband leans back feeling pleasure, overcoming any guilt he may feel for doing this in front of me. I get pounded from behind, while watching her head bob up and down, him playing with her breasts like he used to do with me.

Finally they both come, and I clean up, put my clothes back on, before he comes over to me. The woman smirks at me as she wipes her mouth and leaves. My husband comes over, giving me a big hug, acting like everything is fine, because that's the new normal now. I just get to be glad he takes me home, even if he fucks other women along the way.