question from a new guy

I got my girlfriend to finally try relaxing with other men and she has been seeing a older guy for about 3 months now,and has moved into the role of his slut a lot faster than I thought she would(esp since it took 6 months to get her to even consider being with another).I would love to be fully cucked by her and she has started to become a little Dom with me but my question is...
Is a Dom side comming out or is it mostly because she is being Sub to her new lover and just doing the things he has asks her to do.

probably a little of both

takes most folks 6+ years so if you did it in 6 months then yes, things are moving rather fast!

watch out or she will be gone by 8 months...