Hi, Both are correct, but “He was lying to me the whole time we were dating” sounds more natural and is more commonly used.

Both are grammatically correct, but: "He was lying to me the whole time we were dating." is more natural and commonly used. "He was lying to me the whole time we dated." sounds slightly more formal or condensed, and is less common in casual speech. Use "were dating" for a smoother, more conversational tone.

either or is good. 1. a time frame 2. a course of action