Demonic Portal

okay, so when i was at school, my ex girlfriend and me were hanging out at lunch. after a bit, lunch was over and 5th period started up, and thats when things started going wrong. she wasn't really talking, so i asked her about it, and when i got an answer, i didn't know what to say.

apperantly, she's jealous of one of my friends who i text a bunch, and it hurts her to hear me talk about her.

i have never met this friend in real life, and we are just friends, nothing else.

now, my ex won't talk to me because of all this, because i couldn't see she was jealous.

my question is, should i have even noticed it? she was the one who broke the relationship off, so should i have noticed she was jealous? should i have been thinking that it might make her jealous?

or is it her in the wrong? is it her fault for expecting me to know that she was jealous, even though we're not dating.