My roommates had a party this weekend. I didn't attend cause I had previous engagments with my parents to have them come up and see the town I live in now.

Well they decided to invite someone I had a thing with a while back..... To elaborate this "thing.."

I have been in a relationship going on four years now with my current SO. Me and her hit a rough spot in our relationship and I was feeling a bit insecure so I started to talk to this other girl, let's call her NotSO. I flirted with her while still in a relationship with my current SO and just kind of lost my mind in that world for.. a week at most. I got my shit together and realised I wasn't trying hard enough in my current relationship and cut ties with NotSO before it got too deep. (All we did was flirt with each other but no touch/kissing/anything.) 

I broke down and told my girlfriend about it and how it happened. She got over it and understood just as long as I didn't hang out with her / see her(NotSO). Understandable.

WELL, my roommates invited NOTSO to the party... Without telling me..

I understand they want to hang out with her cause they work together, but I can't help but feel pissed off about it... Should I be mad? What should I do?

All I really wanted was for one of my "friends" to at least text me, "Hey, soo NOTSO is at the party."
user
Came home to someone I almost cheated on my current SO with at my roommates party(them fully knowing everything.) Don't know how I
assistant
My roommates had a party this weekend. I didn't attend cause I had previous engagments with my parents to have them come up and see the town I live in now.

Well they decided to invite someone I had a thing with a while back..... To elaborate this "thing.."

I have been in a relationship going on four years now with my current SO. Me and her hit a rough spot in our relationship and I was feeling a bit insecure so I started to talk to this other girl, let's call her NotSO. I flirted with her while still in a relationship with my current SO and just kind of lost my mind in that world for.. a week at most. I got my shit together and realised I wasn't trying hard enough in my current relationship and cut ties with NotSO before it got too deep. (All we did was flirt with each other but no touch/kissing/anything.) 

I broke down and told my girlfriend about it and how it happened. She got over it and understood just as long as I didn't hang out with her / see her(NotSO). Understandable.

WELL, my roommates invited NOTSO to the party... Without telling me..

I understand they want to hang out with her cause they work together, but I can't help but feel pissed off about it... Should I be mad? What should I do?

All I really wanted was for one of my "friends" to at least text me, "Hey, soo NOTSO is at the party."
user
Roommates invited friend, who I had a thing with, to party.... I had a thing with someone else but I don't want them
assistant