Just be straightforward, brief, and kind. Use 'I' statements.
“Person, this relationship has been great, but I'm no longer happy, so I am breaking up because it doesn't work for me anymore.”
Don't offer reasons that she will claim she can fix: “This relationship bores me now.” “I can be exciting! Just tell me what to do!” Do not let her manipulate: “I'm not happy anymore.” “Oh after everything I've done, now I'm not X enough?” Etc. Don't be drawn into conversations that cannot be resolved.
Just be kind and consistent. “Person, this is not about you or your personality or your worth. It's about me not wanting this anymore. It's not your fault, and it can't be fixed.”
For real. The vagueness of the issue leaves it really ambiguous. How serious was this issue?
Just be straightforward, brief, and kind. Use 'I' statements.
“Person, this relationship has been great, but I'm no longer happy, so I am breaking up because it doesn't work for me anymore.”
Don't offer reasons that she will claim she can fix: “This relationship bores me now.” “I can be exciting! Just tell me what to do!” Do not let her manipulate: “I'm not happy anymore.” “Oh after everything I've done, now I'm not X enough?” Etc. Don't be drawn into conversations that cannot be resolved.
Just be kind and consistent. “Person, this is not about you or your personality or your worth. It's about me not wanting this anymore. It's not your fault, and it can't be fixed.”
Good luck OP.
We can't tell you what his deal is since we don't know him. Try talking to a therapist.