Getting bored with him

Hey - how are you all today? Hope you are doing okay =)
The guy I have been dating - and who was the first (and only) one to watch me and Marie kiss - called me today. I hadn't spoken to him since newyears evening. To be honest I am not very interested in him anymore... I can't put my finger on any reasons why - I just don't find him exiting.
I don't like telling it to him - but it would also be unfair to pretend something...
And this is not the first time this has happened to me - I wonder if it's normal? After some time I just get bored.
It's like I am afraid to.. hmm.. get too seriously involved?
Well, I better talk to him about all this before he starts planning our wedding