In your case your mother took her own life. That is a concept that is beyond the scope of understanding. I am sure that questions are flying faster than the speed of light in your mind. The last question explains to you the natural propensity for which we are quick to assume blame. Not trusting your own self.
Guilt is a by-product of someone's suicide.
You are fearful that your boyfriend will suddenly stop loving you. What I sense is that you are stronger than your mother in a lot of ways you do not give yourself credit for. Knowing that there is a chance for such issues to exist in your life is half the battle. Half the battle is being forearmed. Being forearmed is being forewarned.