Retroactive Jealousy. And none of hers.

Hi. I am Aman,24 year old guy from delhi working in govt sector. I am in a live in relation with a woman 4 years elder to me. We are living together for the past 7 months. My problem is I don't know how to deal with the past of my gf. To add I was a virgin but she wasn't when we met and I knew this. I thought I could deal with the thoughts of her past getting intimate with three other persons before me. The last one being a no strings attached relation with a man 10 years elder to her. Lots of sex was involved. Now I get sick in the stomach for the thought that I will never be her first. That other men know her in a way that I wish only I knew. Whenever we get intimate the thoughts of her in bed with others makes me sick. Kindly help me. I know it's my problem to deal with and none of hers.