If she is your girlfriend you have already determined she is above a lot of other girls. You determined she is a keeper and its not easy to just show her the door as people here are saying. Theres a million reasons as to why your girlfriend might be putting on weight.
The best thing to do is talk to her and let it be known she is not going down a path that is acceptable to you. Don't sugar coat it but don't be an asshole either. "I am beginning to find you less attractive." is all you need to say and if she starts getting emotional and saying those stereotypical things you know she is going to say just hold firm and don't waver.
What does it say about you as a man if your serious with a girl you can so easily discard?
Better yet, don't let it get to the point where you find her unattractive in the first place.
The best thing to do is talk to her and let it be known she is not going down a path that is acceptable to you. Don't sugar coat it but don't be an asshole either. "I am beginning to find you less attractive." is all you need to say and if she starts getting emotional and saying those stereotypical things you know she is going to say just hold firm and don't waver.
What does it say about you as a man if your serious with a girl you can so easily discard?
Better yet, don't let it get to the point where you find her unattractive in the first place.