Why am I always upset at the person who I thought was the one?

My boyfriend [26M] and me [23F] have been together for around 2 years. I’ve always thought his kindness and love were unmatched. When we lived in the same city, we would often stay at each others places and he always would cook me up a big breakfast, leave me sweet notes, etc. He’s always been great with my friends and family and we have a lot of fun together. We support each other through everything and I’ve always thought he was the one.
Now we’ve been long distance for some time which we were handling great at first, but recently I’ve been struggling. There’s been a lot of little things he does that get on my nerves or make me upset and I’ve communicated them pretty much every time. He always takes it well and understands why I’m upset and says he’ll do better. But he always ends up doing it again. I can’t deny his progress though.
I’ve been trying to get into a grad program for a while and a few weeks ago when I told him I got in, he barely reacted. I had a serious conversation with him about how distant he felt and the lack of emotional connection and also how some of the things he does really upset me and how I can’t take it anymore. He reacted relatively well to this too and said we should get an Airbnb somewhere together to have quality time for our emotional connection. I loved this idea and have been looking on air bnb a lot for a good deal in the city we wanted to stay in (he expressed how finances are tough but he still wants to do it). I sent him a bunch of places, but he never said yes to any of them. He sent me 2 options, both that were less expensive but were literally just rooms in someone’s house, not a private place. He said he didn’t realize and that he would keep looking. I ultimately found a place after looking a lot more and had to put it on my card. He did say he would pay me for half though.
I’m just feeling frustrated and at a loss of what to do. I told him it upset me and that it seemed like he barely looked, but I’m honestly so tired of telling him that he upset me about something. I don’t want to resent him or think that things might not be working out because that’s the last thing I want. I don’t know if I’m just having extreme negativity bias or if he just keeps messing up small things or if the honeymoon phase has gone and we’re not as compatible as I thought. Any advice would be greatly appreciated, especially if people have successful relationship experience with long distance or getting past cumulative resentment over lots of smaller issues. Sorry for the length of this post, thank you for reading and for any advice!

TLDR: Why am I resenting the person I love, and how do we move past it? Is it negativity bias, distance, or is he the asshole?