Can anyone give me a suggestion on this?

I've been goin out with this girl for 4months now. and shes absolutely amazing. We get along great, do stuff together, no problems, the love is so strong and everythings there.. but theres this one and only problem..her past history with other guys, everytime i think about it I go beserk, im a very i guess u could say territorial person. and to think of someone touchin her besides me gets me enraged. it just makes me angry because its the only thing in our relationship that isnt right and i want to fix it. does anybody know any techniques or something i can use to forgive and forget? thanks a bunch