I need relationship help, unfortunately. :(?

So, I'm dating this girl, and she's one year younger than I am. We're pretty happy, we have sleep overs, hang out a lot, and pretty much have a merry old time. It's just, I find that we both get pretty jealous over the other. She talks about her ex-boyfriends and her ex-flings and their, er, "adventures" sometimes, which well, I don't have any past "adventures", so I get a little upset. And for her, my best friend is a girl and I kinda broke up with my ex and started dating her right after, but me and my ex are still really close, like, good friends. I don't understand why we can't just, be hunky dory if that makes any sense? Can anyone give any input, or past experiences? Thanks in advance.