This is sad. I know a person like this too.
You can lead a horse to water but you cannot make them drink.
You also have to think about YOU and what your boundaries are. Don't YOU get sucked down with the sinking ship.
If you decide to hang on to the friendship and have figure out where your limits are... stick to your limits and try to be supportive within that range.
It may take a few attempts before she can actually break totally free. Offer her an ear, a place to crash, encouragement to seek counseling, but don't nag. Also don't get sucked into drama.
Hours of phone drama going nowhere? Learn to cut her off after 30 min and play the broken record. "I'm sorry there's all this stuff... I really think you ought to talk to a professional. This is beyond my skills." Don't be her sounding board, don't analyze with her. Because then the abuser is sucking up her life as well as yours! You won't get those hours back.
Dumping on you may help her temporarily... but if it is chronic -- in the long run you are enabling more than helping. Point her to the pros firmly. They can help her better.
Do you think she's stuck in the emotional abuse cycle?
http://www.lilaclane.com/relationships/emotional-abuse/
Instead of focusing on him... focus on HER. Encourage her independence so she's not more sucked in by him. Her OWN bank accounts, her own job, her own apartment, her own cel phone, her own car/bike etc. Celebrate the good she does for herself in that area.
If she wants to date him you cannot do much about that. But you can encourage her to maintain her own space, life, identity. Encourage her to date others. Play the field. Give herself a chance to stay open.
Emotional abusers try to cut off the victim from support from friends and family, the purse strings, transportation, etc. They play the "If you really loved me..." card and ask for a lot of "proving" from the victim. Just loving them isn't enough, they have to prove they love them over and over and over. Mainly because the abuser likes to see they can make the other person jump to their bidding.
She may think that because it isn't physical it isn't "real abuse" yet. It does not have to be physical to be abuse. (And her depression may be exacerbated or caused by him. )
There are local hotlines --- I don't know if you want to give her the numbers. She may or may not call.
And if you have to take a break from the friendship... do it. Save yourself and do a friend break up. It may or may not cause her to see the light, but YOU need to look out for you. Don't need some creepy guy coming after you too.
A.