They're fairly common, they want to drag others down with them for comfort more or less.
Yep, its not that they want to help, but drag you down to your level. As an equalizer. Its not outright out of evil motives, but selfish ones. So they have a "friend". If they would get back their life together, they would leave you, because theres no common ground anymore.
The only way to fix that if you want to stay with that person, is to both get it together or if you dont mind, fall into the abyss together.
Edit: Just to prove the point, her friend was devasted on page 10 after second FMC left her.