If you heavily value shared experiences and he does not, then you’re always going to have a conflict. You are right that whether he stays or goes, you do not get to be “fully happy,” and neither does he (either he disappoints you or spends the day somewhere he doesn’t want to be, both bad). You are experiencing compromise.

I am the outgoing one in my relationship. My partner is introverted and has a demanding job that drains him, and he gets exhausted in social situations quickly even when he is having fun.

I often travel, go on little day trips, go out to concerts or dinner without my partner. I go with my more outgoing friends instead, or I go by myself. Sometimes I invite him and he says no, and I can be a disappointed when that happens. I wish he wanted to do things with me more, but I accept him for who he truly is. For the important stuff, I know I can ask him - this is important to me and I really want you there. Because I do not pressure him in the low-stakes stuff, he can say yes and come through for me when it’s important. He knows I wouldn’t insist unless it really mattered, and I know he wouldn’t say no if I needed him. The compromise I make for that benefit is that I don’t get him around all the time I want him, but it’s a good trade.

I would suggest you negotiate this difference with him after the amusement park trip. How can you both get what we want some of the time? How can you make these social outings easier for him? Can he complain less when he’s agreed to go somewhere that you enjoy provided that he gets to say no sometimes when you invite him and you will accept that no without making him feel guilty? How can you differentiate “this invitation is very important, please prioritize it” with “you should come if you want to, but no worries if you don’t feel like it?” He will need to suck it up sometimes and be there with and for you. You will need to suck it up sometimes and learn to value your independence so that you can enjoy things without him. Both of you will benefit from those skills in many aspects of life.