My girlfriend has become fat!?

Ok so i love my girlfriend when i met her she was this fun bubbly sexy girl who every guy loved u would be lucky if she said hi to u. well we've been dating for about 6 mounths and last month was home coming 5 mounths ago she picked out a dress for it well that day of the dance i came over to her house when she put it on and i did not fit what so ever. like im talking the zipper broke it was a mess. at the dance she wouldnt dance with me all she would do was sit and eat the whole time and when i did dance with her i felt rolls of fat along her waist. ok so a week aftr the dance i sat next to her put my arm around her waist looked down at her tummy and noticed her waist increasing day by day and she always eating junky food whenever i see her. her pants r getting tighter on her and her stomich is hanging over her pants. for a couple days ive been seeing her pants unbutton with her trying to pull down her shirt to cover her big belly bt it keeps rising up. i hate to say bt i need my sweet heart bak