"Bipolar" is a word that is bandied about with increasing frequency. Many people who have no qualifications to determine whether someone has a mental illness are labeling others with the Bipolar word. Only a qualified, licensed mental health professional can do that.
Some people have difficulty handling strong emotions. Does he often shut down when you try to discuss something important with him, that carries a strong emotional tie? Other people have trouble taking responsibility for their own thoughts, feelings and actions, and blame others by telling them they are the one with the problem. Does that seem to fit him? If any of scenarios are the case in your relationship, some couples therapy could be helpful to improve communication and problem solving skills.
But also consider the possibility that he could be on to something. Are you often moody? Do you feel really up one week and really down the next? Are you easily upset? Do you feel unstable or out of control? Do you have impulsive behavior, making poor decisions frequently, many choices that you later regret? If you answer yes to those questions, then perhaps seeing a therapist would be a good start. A therapist can help to diagnose the problem, provide coping skills and other treatment, and give you a referral to a psychiatrist for medication, if needed.
If that is not the case, and you don't believe that you have some type of emotional or psychological problem, then you need to have a serious discussion with him, telling him that when he says things like that, it is very hurtful. Let him know that instead of blaming you, he needs to try to express his own feelings of frustration, anger and hurt.
In any case, couples therapy can help to improve your relationship with your fiance. I strongly suggest that ALL engaged couples have premarital counseling before tying the knot.
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