I'm going to record a school project solo instead of working with a lazy partner
Why can't you work with your partner?
He's not really serious about this project.
It's hard to work with lazy partners who just want everyone to do their work for them. If it's still possible to do so, see if you can split off and leave this other person to handle their own solo project, just as you are doing.
I just have to tell him what I've already done.
Good on you for not letting him bring you down. Life is full of people, and school prepares us for all those kinds of individuals. I hope you can manage well on your own!