I feel like i’m outgrowing my best friend.

There is a whole backstory of course, considering we've been friends for three years and got through our last years of high school together, but I'll save that and just jump into the things that are recent.

I (18F) guess I feel that I'm maturing more than he (19M) is. I don't mean that to be egotistical, but it will hopefully make sense when I explain.

So in my latest posts I talked about how he works with me and some issues we were having there. But TLDR, I give him daily transport, and he is very unpunctual on a daily. I ended up having to come into work later one day, he was a no call no show, and also consistently is asleep, not ready, etc. when I get to his house to pick him up.

Since then, boundaries have been put in place but it's been recent so I can't really say if it's improved, but anyway.

Moving on, I'm often responsible for watching my siblings for my mom when she has work meetings and whatnot. Friend, me, and another friend (not that relevant to the story) all planned to go to the gym not knowing that my mom was going to need me for something yesterday.
I told them that they could leave and didn't have to wait for me, because my mom was most likely going to be home late as she was already 45 minutes away and still had to finish her work and grab food etc.
They kind of just sat around and finally I just was like, "you guys can just go it's fine."
I sort of felt like a burden because they were just sitting around and waiting for me, knowing it was going to be quite some time.
Finally, friend was like "okay, are you sure? we'll talk."
then started to freak out with anxiety. I just kind of looked at him funny and was like "okay? about what?"
And he sort of just refused to tell me. I didn't push it and just let it go, then he left. However I had a lot of anxiety about it.

Flash forward to today, he texts me and asks if I want to go to the gym. I told him sure and he brought up having a talk again. I told him okay but I didn't really say anything else or bring it up again. We were at the gym for like an hour and then he wanted to leave, still not bringing up whatever it was and furthering my anxiety.
We finally got to the car and I'm just like, "okay what is it."

He told me that he felt I didn't appreciate his interests enough. I was just kind of like "really?" because I thought it was going to be something like crazy serious. He was going on a tangent about how I didn't show any energy about it and I'm just a little baffled... because he takes 0 interest in what I like to do either. I don't think he could even name any of my hobbies, besides for going to the gym and playing video games. The main thing he brought up was his music and how hes so passionate about it, yet every time I play a song I like he doesn't even listen to it or will complain about it.
Either way, I'm confused as to why he thinks I'm obligated to like the same things he does.

After this conversation, he just sort of ends it with "I'm glad I got that off my chest." so I assumed that was all he had to say, so I was like "oh- that's it?"
And he was like, "well... not exactly. but i'll talk to you about it later."

This is what is leaving me confused. I talked to my mom about it and she said that he's holding it over me and using it as a form of manipulation. Robin Hooding, I guess would be the slang term for it. I didn't think about that until she said it, and I can't help but agree.
She brought up the point of, "how would he feel if you did the same thing?"
and I sort of thought about it. She said I should do the same thing, text him and say "hey, whenever you're ready to talk, I have something I want to say, too." and when he decides to talk, reply with "oh, nothing. I just wanted to know how that felt."
She says that he's doing it on purpose, that he knows it will give me anxiety and that's how it’s manipulative, and "this isn't fourth grade anymore."

I can't lie, it's a good idea and I don't disagree, but I know how I'll feel after, probably even more anxious. He's still my best friend despite all of this and I just don't know how to feel. If I lose him I have no friends. I'm stuck between a rock & hard place and unsure what to do.

Any advice is appreciated, and if you tell me to just take my mom’s advice I’ll take that too lol. I just need another angle from someone who doesn’t know either of us personally.