My BF suddenly talking to me much less

I've been dating my boyfriend for half a year now but known him for longer. We both just finished our A levels and we're both now working 3 days a week and I'm also going to uni part time.
I'm fully aware that we won't be seeing each other as much and we'll both be much more busy but I still try to message him whenever I have the chance but don't feel like he gives me the effort back. Since I've known him, it was normal for him to not be on his phone for a couple of hours at a time and he would always reply to me but now he's suddenly started talking to me a lot less like 3 messages a day. He always picks up straight away if I call though.
I've tried talking to him about this and how I would appreciate it if he just took a few extra minutes to catch up after he got off work for example but nothing's changed and it's making me upset. I feel like I'm being too needy but I just want to be able to talk to my boyfriend because I love him and enjoy talking to him.
Also he's going to see a comedy show with his friend (who he's always talked to constantly everyday) who recently got cheated on by her boyfriend and taking her ex's ticket and all he's said to me about her is 'I definitely don't like her and I'm pretty sure she doesn't like me' which was really odd to me.
I would really appreciate any advice to properly communicate how I'm feeling about everything in general because he's great and I don't want to lose him I just don't want to be stressing out and overthinking everything.