Someone being emotionally distant.
Signs of emotional abuse in prior relationships.
Unwillingness to respond or get intimate.
Controlling behavior.
Someone with anger management issues.
Previous substance abuse.
Signs of prior abusive behavior.
Wants a significant amount of personal space.
Notice red flags early by going on dates and taking things slow. Any romantic relationship has issues. Although, go with your gut feeling. If you think something is a serious red flag, go with that instinct. Understand your own deal breakers and follow them.