How do I, 19 F, fix my relationship with my boyfriend, 20 M?

for context, i, 19 F, and my boyfriend, 20 M, have been together for 3.5 years and have been very happy throughout our entire relationship. we have been together since i was 15 and we have been eachother’s first everything. we have always had a deep connection and a great relationship, my girlfriends would often say things like “i want a guy that treats me like (blank)” or i need to find my (blank)” because of how great our relationship was. now, our relationship is still good, and im still happy, but it’s just not the same as before and i don’t know what to do to get our spark back. i have told him that i feel like he doesn’t treat me the same as he used to, and he seemed like he really cared and wanted to fix it, but there just hasn’t been much change. i’m scared that we’ve outgrown our relationship. there’s been a lot of times where i’m upset or crying when leaving him and i don’t get a text and the phone doesn’t ring, but then the next morning he always apologized and tells me he loves me. a lot of the time when i want to go out somewhere he will agree, but then he doesn’t act like he is having a good time. he acts bored/uninterested, and when i bring it up he says that he’s just tired from work, but even before he was working again he was acting like this. i don’t feel special or have butterflies when hanging out, and he doesn’t compliment me as much either. he is a great boyfriend other than these things, i’ve never had to worry about cheating or anything like that, he’s never called me a bad name in my life, he’s very respectful and kind towards me 90% of the time. for context as well, i’m not just a girl that spends his money or stuff like that, if anyone assumed that. there was a while where he wasn’t working where i was paying for everything and now he’s working again so he’s paying for our stuff again. i don’t mind pitching in when he’s down. i just need help. i love him so so much, there is nobody else i want to be with, and i don’t want to start over with somebody new. my friends just tell me to cheat, but i don’t want to be with someone else, he is the only person i want to be with romantically and intimately. but im not feeling reassured/secure in our relationship right now. can someone please give me some advice? my mom said i should just greyrock him until he realizes how he’s acting, but i dont want to do that. please help.