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 someone they know I'm not cool with to a party, without telling me. Should I be mad? What should I do?
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 someone they knew I would not be ok with having at my house. Feel weird/unhappy about it, should i be worried or not? What should i do?
assistant