OP, hope you don’t mind, I just wanted to chuck my 2 cents in here as I felt a similar way about my partner and very recently had a situation that made me think differently. I don’t know if it will be as relevant to you, but throwing it here on the off chance it is 😊
he was/is my best friend but I was in a very similar position, thought processes etc to what you’ve described. But as you have suggested I don’t necessarily want to up and leave, because i felt I didn’t have a reason to - he is a good person, at the end of the day.
Something additionally happened between us that led to us speaking to a relationship counsellor. And it was brought up to us both to have an investigation into our love languages. I discovered that mine were things like quality time, which made a lot of sense to me, as I’m the one who plans the dates and dinners and trips away etc, etc. I felt like an AH thinking of it for a while feeling a bit materialistic, and then it was explained to me that it wasn’t about the physical thing or the monetary value, but the fact that someone had put the time and effort in. And that was exactly what I felt I was missing. as for my partner, his is more he appreciates greatly the little things like a cup of tea brought to him, a bath run, filling the car up for you, etc etc. and he was always doing those things for me, even though I wasn’t looking for them.
so we both realised, we were doing things we would have appreciated ourselves for the other person, which was lovely, but that we weren’t getting what we were looking for from the other. So we talked about it and we tried to make a conscious effort to do things the other person was maybe needing and not getting, instead, whether or not they felt important to us as individuals. it’s been incredibly helpful. I just wanted to put it out there as a point of conversation between the two of you, as my partner hadn’t realised at all really that i felt like I wasn’t getting something in the way I needed it.