。
I want you to keep your promise.
Literal
Promise [obj-を] keep-[desiderative-て欲しい].
~て欲しい (te-form + 欲しい) expresses 'want someone else to do X' — distinct from ~たい ('I want to do X myself'). An important split for learners: Japanese uses separate grammar for own-desire and other-desire. The subject whose action is wanted is often implicit in conversation.