Love and life advice [NSFW]

Hi there! I am "holly" and i am in my mid 20s and British I have always considered myself straight. I have a long distance GF of 9 years, about 3 months ago we hit a issue in our relationship involving her hiding me from her family. other then that everything was fine, when we met up the sex was..okay and fun. About a month ago i met this guy while playing a video game we got talking and shared skype pics and stuff became good friends really fast. Then things got weird. We started discussing fetishes and turns out he likes crossdressing but also likes being dominant, he started making jokes about making me wear diapers for him and me being his princess, normally id have ran, but i played along, i started to enjoy they way he spoke to me like that, i felt safe, cared for, loved. I noticed that i had feelings for him and...WANTED this. so once night i let him take control over skype...and it was the hottest "skype sex" ever, better then the real thing with my GF. A few days later i found him playing submissive to another guy, i was so angry but i didnt understand why, we hadnt said we where together, we couldn't be together i have a gf. it ended in a argument and he said he would stop talking to that guy. i find myself worrying all the time they he still is talking to him though. i dont really understand my feelings for him, but i know i love and want him. i don't know what to do at all. any advice is welcome before i go crazy!