I totally understand. Of course we want to make our SO feel sexy and good about themselves but for sex to be the only form of validation for them is not healthy. For either of you, truly! I've actually been where you are and it took a severe toll on my mental health. I wound up taking those issues into my next relationship as well. So, in some form of self fufilling prophecy when you aren't enjoying yourself, your partner notices. Sometimes they become fixated on pleasing you and with each failure they grow more frustrated and determined. That pressure to validate consumes you and then no one is happy!

Toys are a great place to start and can be a shared activity as well ( I suggest using them yourself first to get the hang of it). As for poly stuff, I'm actually with you on that. It works for some people, but it's definitely a tricky subject. Start spending some time with yourself intimately and learn what revs your engines so you can share it with your partner.

If it's truly too much to handle, you are entitled to your boundaries and bodily autonomy. You do not OWE intimacy to your partner because they want it. In fact, if they are so fixated on the physical stuff they should be going above and beyond to ensure your pleasure and desire to participate.

You seem cool, and I hope I offered something of use to you here.