Think about this differently: as you have more relationships you learn what you can tolerate and what you can't. The less experienced you are, often the more patient you are with red flags. I'm sorry if not owning all of a person's firsts makes you feel inferior, but that has to do with your self esteem, which is probably what undermines you and makes you insecure. She can love you more than she's loved anyone ever, even if she's loved someone before.