If your girlfriend is actively struggling with bulimia then it is a very serious matter. The question you asked was related to how you can better communicate with her and I will offer you an answer but first it’s important that you are aware of the sobering reality of eating disorders.
Eating disorders can be deadly. They have the highest mortality rate of all mental health disorders. Bulimia can cause significant physical damage to the body. The forced vomiting associated with bulimia, for instance, may cause tooth decay that can result in tooth loss. Other physical health concerns common among individuals with bulimia include dehydration, scarring of the hands, electrolyte imbalance, low blood pressure, irregular menstrual cycle, esophagus or stomach rupture or bleeding, heart problems, along with other possible serious health issues. The dangers associated with bulimia and eating disorders in general cannot be overstated.
You indicated that she is unable to discuss emotional matters with you. It may take some time before she is able to do this. Now is not the time to try to force her into discussing what she apparently is not ready to talk about. Try not to take her lack of communication with you personally. The reason she may be unable to tell you what’s bothering her probably has nothing to do with you. It may be that she has trouble communicating in general or she is ashamed of or feels guilty about her behavior (this is not uncommon among people with eating disorders).
The way to handle this situation may be to tell her what you wrote in your letter, in a very direct manner. You can say to her “I know that you are hurting and struggling and I want to help but even if you are not ready to share your feelings with me I am here for you no matter what. I will always be here for you and I love you. You are safe with me.” You can reinforce your words with actions and you can do this by literally being available to her when she needs you or requests your help.
Because of the seriousness of bulimia, I would also strongly advise you to encourage her to seek professional psychiatric assistance. In fact, the biggest help you can be to her at this time is to assist her in finding an eating disorder treatment program. There are many helpful treatment programs available that range from group therapy to cognitive behavioral therapy, and others. In some cases medication can help also but your overarching goal should be to facilitate the process of finding professional mental health treatment. I hope this helps. Take care and thank you for the question.