I know exactly how you feel. For this reason I was single for 13 years. Now I'm in a relationship for 4 years and STILL feel like this. Did you have negative experiences in the past to make you so distrusting of men? Maybe therapy will help you to get insight in the why you feel this way. I have therapy too, with me the reason is my dad left us when I was around 5 years old and also because of long term bullying.