It's a mixture of 1, 2 and 3 perhaps . It means as much as you give it importance.
-how long yall dating now?
-I see the word college. That means she is on the younger side? How old is she?
- I also wonder how and why she brings this up. You both are Netflix and chilling and than boom, "Jimmy is kinda hot ", out of nowhere?
- I also wonder if she just knows him or does she actually is in contact with him?
-Basically I wonder: do YOU feel like you should be worried?
It is what it is though. You'd be naive to believe she'll stay with you for ever ever. She might be wandering around and maybe you gave off so much friendly vibes by now she (unconsciously) puts you in some sort of friendzone / "more like a brother" position where she feels comfortable enough to tell you something like this. it's on you to (subtly and unconsciously if needed) regain or improve frame and show her you are her best option for now..if the damage isn't already done.
Generally I would say dont worry, but it does seems kinda disrespectful. There are plenty of hot people ,no need to mention that and fck with your head. Still I would take a even DEEPER look and analyze how you behave around her and how she reacts to you.
You gotta be honest and look back how it all went down; how you met her, who initiated the relationship, her past . Only then you will be able to come up with a sincere answer to your question.
I'll end with a (in)famous Chris Rock qoute;
You were NEVER her first choice