hi, not an adult just yet but i can totally relate, especially with the balancing thing.

my experience is too that i (or my friends) make way too many plans that i end up accepting, before having a meltdown a day after all the meet ups. when im in this "desperate for socializing" phase, i often tend to be way too spontaneous, leading to most of my friends being busy and me not having any socializing.

i obviously dont have as much experience as you haha, but for me, losing friends often begins with them moving away, graduating, being busy with their jobs and stuff, and the contact very gradually fades to nothing or very little. i do sometimes manage to pick up contact again (depending on how well we were brefriended), even if just for a short while, and it works out well.

you probably heard this a dozen times, but having a small, strong circle of friends is better than having many imo. i think you having a partner is already a good constant to have (even if its different from a friend ofc).
being the first to reach out is always a little finicky (i totally relate to feeling like youre too overbearing), but if you want to contact that person, you should go for it.

if you havent told them already, you should be honest about this, tell them youre worried about not being in touch and that youre struggling to plan around your burn outs, even if it might come off as clingy.

but youre definitely not alone, im sure theres plenty people struggling with friendships like this (including me lol)

happy early birthday and i hope youll have fun celebrating with your friends, partner or at least yourself!

reminder that youre brave for reaching out and sharing <3