The Feeling of Insecurity of Myself

I admitted that I am very insecure of myself. Someone said to me, "If you know you are good enough for your bf then you should not have to worry about him leaving you for someone better". But most obviously I can see why, my insecurity is ruining the relationship, I don't trust my partner to be faithful to me, but who can blame them with the way I have been policing his every move.... Has it become illegal for my bf to hang or converse with the opposite sex because they are in a relationship with me?? Should I fix myself? I think, if I fix myself then I would not have to be insecure and jealous over my bf.