Going against the grain here but he could be genuinely feeling like he's missing out and needs to experience a bit of excitement.
Sex and sexuality changes through the years, and the shame, self-censoring, pleasing your partner (instead of you), conforming to others expectations of sex can all stop you from fully developing and experiencing all that life has to offer.
People will roll their eyes and chalk it down to Mid life crisis but it's not. I have personal experience of having what was a very long term vanilla sex life with one partner, he got bored, wanted to experiment and never told me (I too was bored but happy), and he ended up cheating multiple times to experience things he wanted to. If he had sat me down like yours had and told me of his feelings, sure it would have been a shock but maybe it would have helped. He didn't, lived a double life, it came out, lots of hurt, relationship destroyed, I became physically ill from the stress, and took me years to even contemplate dating.
As it happens, I met someone who opened my eyes to how sex can be in it's true form. When you really let go, free of shame, bad experiences and truly want to pleasure someone and be pleasured in return. There's absolutely no going back for me. I'm having the best sex of my life. I'm a kinky so and so now. It's incredible.
Your DH is giving you the chance to jump on board with his new found lust for life. He wants to experiment and experience with you. He has opened himself up and made himself vulnerable to shame and rejection.
If you want your relationship to work with him you need to listen to him and enter a conversation with an open mind. Discuss what he wants, what excites him, and also what excites you, what do you secretly harbour. Read articles on sexuality together, think about how you can safely explore with boundaries and have fun, that's the most important thing.
But I will say one thing, once you have a sexual awakening like your DH is wanting, it's very hard to go back to things before.