pathological jealousy and insecurity

Hello, my name is Sophia and I am 25 years old. I am in a relationship for almost three years now with a man that  is three years older than me and he is a hypnotherapist and mentalist... he is from el Salvador and came to Greece to participate on a contest. We met, fell in love and he decided to stay here with me.. We are very in love but we have been through some issues cause in the beginning of the relationship I had been unfaithful (kissed one guy once) and I was flirting. We almost broke up but we did not... But his behavior was very changed after that for a long time. This was almost 2 years ago. Since then I have become very afraid of losing him. I have become pathologically jealous and very insecure. I am controlling him and even if he speaks with another girl I lose the world down of my feet. He has tried to help but the more understanding he was and the more he did for me I wanted more and nothing counted... I ended up not trusting and believing him again. He even stopped using a mobile and I had access to all his emails and Facebook. Now I do not anymore cause he could not handle it anymore and stopped sharing them with me.. I am pushing him away but I cannot stop... And now he has to leave Greece for 15 days to go to Italy for another show and I am under panic. I am going crazy not knowing what he will do there. Why can’t I trust him? He never did something not worthy of trust and in the beginning of the relationship the first six months before the crisis we had I trusted him more than anyone.. I was feeling completely safe in his arms and he was my shelter... he made me feel peaceful and I loved it... he was my best friend and I could speak to him for everything and ask him anything.. Now it is not like that and I know I am the one to blame.. How do I stop being so possessive and jealous? How do I trust him again?