<human>: Condense the text into a few key points

Bit of background on my girlfriend: She's liked me for ~3 years, we started dating 19 months ago. She comes from a home with some problems, from what I gather - she doesn't like to talk about it much. Her father is not present, and a jerk, she lives with her mom and stepdad.

She's always been insecure about herself, which has resulted in her being possessive and jealous of me. Recently she's started gaining weight, resulting in her being even more insecure about her appearance (and stemming from that, the strength of my commitment to her?).

This has been the case for a while, but its been okay, for the most part. Recently however, I was in a school play and onstage I said "I love you" to another girl.

My girlfriend said: "something broke inside of me when i heard you say it to someone else i cant explain it and since friday i've been having all these crazy thoughts," Fllowed by: "i love you but i feel horrible about us for some reason i cant explain it i cant figure it out myself... i'm insecure". She then asked me to remove all the pictures from the show where I'm with the girl in question from my facebook timeline. I acquiesced.

I suggested we talk to a school counselor together but she seemed hesitant and changed the topic.

In my mind, she has nothing to be insecure about - I find her incredibly attractive in every way and am very committed to her. I've told her this, but it doesn't make a difference. So guys, what can I do to make her feel better again?
<bot>: I said "I love you" to another girl onstage, as part of a school play. My girlfriend says it destroyed something inside her. What do I do?