There's a big difference between constructive feedback and nitpicking criticism, and social worker Kristen Okrzesik says that if your partner is constantly telling you what not to do — or, conversely, not supporting what you do want to do — then "this can be a sign that they want to change you to their liking."
Furthermore, people who put you down, make fun of you, call you names, or otherwise criticize you in ways that are denigrating or make you feel bad are, most likely, not people with whom you'll have a healthy relationship. Okrzesik recommends paying attention to how the other person makes you feel: "when you are hurting, stressed, or dealing with frustration, are they supportive, or do they make you feel worse?"
Stephen Stosny, Ph.D., explained in Psychology Today that criticism can cross the line into being destructive when it focuses on character (as opposed to a specific behavior), infused with blame, not focused on improving a situation or behavior, based on only one 'right way' to do things, or belittling.
Such criticism often "starts out on a low key… and escalates over time," Stosny writes, but this pattern can send a couple into a downward spiral filled with ever-increasing resentment: "the criticized person feels controlled, which frustrates the critical partner, who then steps up the criticism, increasing the other's sense being controlled, and so on." So, if your partner seems to find little ways to criticize you, be forewarned: this can escalate into a bigger problem.