I completely agree with Brittany. You have reason to be concerned, especially if you see her doing the same things as you. Like Brittany suggested, maybe going through the healing process together would be beneficial. Also, you say you don't care about your bulimia because you are considered "overweight", but you need to realize that vomiting repeatedly on purpose to empty your stomach causes your stomach acids to come up as well. The more you do this, the more acid you have in your esophagus and the more medical issues you will see.
Overall, talk to your girlfriend about it. If you haven't already, tell her that you are bulimic and you know how hard it is.
Always ask questions when you need to. There are loads of helpful people here.
Good luck. <3
You've been dating her for three years... You have a reason to be concerned and she should realize that. Don't be intimidating, just let her know you don't want her to hurt herself and that you care too much to see her do this. Does she know about your bulimia? Are you getting help for it? Maybe you should get through this together. Hope this helps.