Fear of losing him

my boyfriend and i have been together for almost 2 yrs, his gf before me cheated on him and he has some trust issues. we both hate her. she used to be one of my best friends and he moved to my school to be wit her but after she messed things up with him went to me and we got together, throughout our relationship we have had some troubles with her bothering him. she txt him a few times, she even called him. On myspace she had written him and now im hearing stories of her asking his friends if he and i r truly in love because she misses him. she cried over him in front of her friends and also his, and me and him have been together for almost 2 yrs, and she still is bothering us. I just have the fear of losing him. when she first cheated on him they were on and off hooking up and i was hooking up with him also everytime we got ready to start something serious and he would go bck to her he played with me and he broke my heart but in the end i was the one who got him. I think of that same pain i felt when he would go bck to her now that i hear about all this i feel it again. shes gotten ugly and gained a lot of weight and her personality is also ugly. I fear of him ever tlking to her or if we ever break up that he will start seeing her or jus start tlking to her again. I hate her so much and having her mess with my bf is bugging me so bad and she won't stop. is it normal that i feel this way. should i be so worried. things with my bf and i havent been very good so im jus scared. Please help me.