My girlfriend made a comment...?

[L]

It seems she still has some kind of feelings or attachment to her ex Alex.
If you are uneasy and stressed out over this, talk to her properly and tell her about your doubts openly.
If she still insist on being in contact with Alex, then it is up to you to stay in this r/s or not.
Do you trust her enough?

You stated that you met her through Facebook, which shows that she might meet her ex or any guy through Fb, just like the way you two met.
Since she is still attached to Alex, there's a possibility she might leave you for him.
I mean, if not, why the hell does she still want to keep in touch with him, even as a friend?

It is really not fair to you since you have to delete your exes while she is still keeping her ex, Alex.
If you are unhappy, and you are constantly stressed out that she might meet Alex or other men since she is so free that she is neither schooling nor working
then why stay? if you are unhappy, leave.
Pardon me, but she seems to be a selfish girl who only cares about herself.
As a girlfriend, she should try to keep you happy not the other way round.