How do you you deal with an SO jealous of your past? I [21m] am her [20f] first.

Happily together for almost a year. I have had one girlfriend before, and occasionally she thinks about it (intimacy, etc) and it upsets her. She does acknowledge that it is kind of an unreasonable feeling to have, so it's not an issue of her not understanding that what's done is done. That said though, it does come up occasionally and I wish I could do something to make her feel less bad about it.

I tell her, truthfully, that she is the first person I have fallen in love with and that our relationship is much different in terms of seriousness than my previous one, but the thoughts of me with someone else still seem to surface now and then. I know it's somewhat irrational, but I still wish that I could do something.

If any of you have experience with this, from either side, I would love your input!

tl;dr - gf wishes that we were each other's firsts, want to make her feel better about my one previous SO