She was about to leave her boyfriend for me

I met a girl about four and a half months ago who has been with her boyfriend for the last 7 years, they both live together but have no children. We speak to each other for about an hour each night and meet up with each other as much as we can. At first i think it just a bit of fun for both of us, but after the first couple of months it has started to become a lot more serious and we both want to be with each other. She has said that she is unhappy with her current boyfriend and it feels like they are more like friends than a proper couple. The problem is the girl is finding it hard to actually tell her boyfriend that she wants to leave and she is worried that she might be leaving a secure relationship, albeit an unhappy one, for a relationship with me which might not last.
Last week she was ready to tell him and had spoken to her mother about leaving her boyfriend, however she spoke to her friends a few days ago about the situation and now she doesn't know what to do. Her friends have said that she shouldnt throw away the relationship that she has for me, as it might not last with me and if she is going to leave her boyfriend then she should not go straight into another relationship. Her friends also seem to think that the excitment of our relationship may dissappear once we are together. I feel like I am now back at square one and quite frustrated as she was so close to leaving him.
How can i put her mind at rest that our relationship will last?

What does she want to do, marry you before she breaks up with her boyfriend?

Another perfect example of someone who won't leave a dead relationship until they've already fostered a new one...sad :P