People who suffer from eating disorders need help and support from their social circle. Give the person your time. Hangout with them, take them to a party or if you are throwing a party, ask them to join you. Include them just like you would include everyone else. It makes them feel supported and loved. Even if they don't want to come or you know they won't, invite them and ask them to join you. They may change their mind someday.
If they are ready to make amends and are making an effort to fix their eating pattern, offer to cook for them or take them to their favorite restaurant. It is not easy to return from an eating disorder. They might have good days and bad days. A part of them will always want to get better, so stay patient.
Enroll them at a hospital or treatment center if their condition is getting worse day by day. Visit them at the treatment center if you are allowed and talk to them about their health. Help them stay positive when the days are dark.
If the person suffering from bulimia is too stressed and their health is deteriorating, help them find support. Make them attend therapy sessions and undergo counseling. Do not force them unless they are severely ill. Talk to their doctor if there is any way you can help or make things easier for them.
To help build their self-esteem, compliment them, and show how happy you are to have them. Making the person feel special helps them find their lost self-esteem. Appreciate them and tell them how happy and grateful you are o have them in your life. Repeatedly appreciating them and being thankful for having them will help them fight the disorder.