AIO or am I just not a priority to my long term boyfriend anymore?

My boyfriend (18M) and I (18F) have been best friends since we were in middle school and dating for 2.5 years. He's been a really thoughtful partner and put a lot of effort into our relationship over the past 6 years. but over the past couple of months, things have changed. It feels like he hasn’t just slowed down because he’s busy... but he’s completely stopped putting in effort.

We’re both busy with exams and preparing for university, but I still try to make time to call him whenever I can. even giving up time for other things. He doesn’t really do the same anymore, and I’ve started to feel like I’m not a priority. It’s gotten to the point where I’m crying almost every day about our relationship.

Last night, I was having a bad anxiety episode and needed support. He said he’d call me back in 10 minutes, (because he was at a sleepover with his friends) but never did call me back. no texts or updates. I cried myself to sleep. This morning he said he didn’t call me because he didn't want to wake me up, which feels like an excuse to me. I've always told him to wake me up especially if I went to sleep sad, and he always used to do that.

I don’t want to seem like I’m a "nagging gf", but I feel really hurt and confused. Am I overreacting? Is this normal in medium-distance long term relationships?