Both sentences are grammatically correct 🙂 You can use them almost interchangeably, but there is a small nuance. “You could have at least talked to me before doing that.” This version is more natural and common. It sounds slightly more direct. “You could have at least talked to me before you did that.” This version is also correct, but it sounds a bit more explicit or formal. In everyday conversation, the first sentence is usually preferred because English often uses the -ing form (“doing that”) after before when the subject is the same. Both are correct, but “before doing that” is the more natural choice in most situations. 👍