My mother once told me this when I was 19 and crying to her about my first love: "Love should make you feel happy, not miserable. You are crying all the time."
I have found that if I am anxious or sad more often than I am happy when I am in a relationship, then that isn't a relationship I should be in. Then I have to gather strength to pull the plug, which is sometimes harder than the anxiety. I have found that if my friends are fretting about their relationships, asking, "What should I do? What should I do?" Then they already know the answer.