Honestly, I see this in my office more frequently than you might think. Partners are rarely on the same page with each other all of the time. Life happens and can get in the way where each of you are going to be on different sexual wavelengths. I’m curious as to what isn’t being enjoyed. Have you two just been doing the same thing routinely during your sexual activities? I would first recommend asking your partner why they aren't enjoying sex anymore, or what about the sex isn’t enjoyable. Discuss ways to shake things up a bit.
If you have a hunch as to what the problem is, perhaps you can take matters into your own hands. Try a different location. It could be a different room in the house or renting a hotel for the night. Depending on where you are located, there are hotels that offer fantasy suites with big Roman bathtubs and walls covered in mirrors, or heart shaped beds that vibrate (corny, but sometimes effective). As for at home, I’m a huge fan of sex in the kitchen. Just be careful of all the sharp edges. Maybe you need a new take on foreplay. Have you tried role-playing? Toys? Maybe adding a voyeuristic act like masturbating in front of your partner and not allowing them to touch you until you say it’s okay. Have you tried toys before, or a new toy? There are several new vibrators on the market meant for couples’ play. If the partner is okay with it, tie them up and tease their body and their mind.
What about you? How do you feel about your current sex life? I’m sure there are sexual acts you’ve considered trying that maybe you two haven’t gotten around to doing. Set the stage, and (with your partner’s consent) bring them into the fantasy. The worst that will happen is that the fantasy falls short, and you two can enjoy a good laugh. The best is that your partner enjoys it as much as you do, and you have found a new way to spice things up going forward. I tell my clients all of the time to stop thinking about it so much. Quit taking sex so seriously. It’s meant to be fun and enjoyable.