<human>: Can you condense the text into a few key points?

Alright so her and her ex-gf broke up before my SO entered college, so about 2 years ago? They dated for awhile, but my SO broke up with her because she was figuring herself out and mainly didn't really want to be physical at the time.

Now, before I got with her she told me she wasn't over her ex. Her ex is one of her best friends, and was, even before they got together.

her ex was in a long 1 year relationship after they broke up and has broken up with that guy, and ever since then they've been hanging out/mostly getting drunk together A LOT. Is it wrong for me to feel something over this? 

so tonight, my SO told me she was going out with her 'ex' and 'ex's friends' for some drinks, so I said okay because her friends would be there and whatever. Then I call and find out it's just them two, alone.. eating and getting drunk together and it's 11pm on a schoolnight.

Is it wrong for me to be mad/sad/confused over this? I trust my girlfriend, but I don't trust her ex. 

extra info: me and my gf had some issues, so right after we broke up she went straight to her ex's place and got drunk/slept there.. said nothing happened and then we got back together. Then her ex texted her saying "I thought you weren't going to get back together with her again?" which I thought was rude of her to say since she doesn't really know me.

I don't know, maybe I'm just insecure. this is my first real relationship. I don't want to be overprotective and tell her she can't see her best friend anymore because of this, but to me that bff will always be her ex in my eyes. I will never get that image of them making out in my head, etc. I know there's attraction there as well.. because they wouldn't have dated before if there wasn't. help.
<bot>: my gf hangs out with her ex-girlfriend alot, and is currently getting drinks with her alone tonight and getting drunk.