This is not a necessity.
Often, the antagonist's function is simply to act as a benchmark for the hero's capacities, his or her willingness and ability to let go.
In Hangover (2009), when we first meet Melissa, it's obvious that Stu needs to break away from her but cannot. As the journey and story progress, so he is able to stop taking her phone calls, indicating that he is increasingly able to let go. Finally, he returns home and breaks up with her.
Your primary goal is to ensure that the antagonist performs it's core function. You may or may not want to overlay that function with character (sympathetic or not).
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