Hi sinking, perhaps I could tell you what I think is going on with you. Now, I am not a professional, but I have made it a point to learn and connect some dots and perhaps what I am seeing in what you are saying might help a bit.

I think that this girl you are concerned about is a sort of reflection of your own pain, that is why you can empathize and on such a deep painful level too. Being able to feel empathy for another person is a good thing, because it can encourage one to learn more about others and at the same time help self too. However, it's important to have the knowledge about what the empathy is saying about yourself. You know she has a need, you know it well because you can identify with it. However, you are right in that even though you want to help this girl, you may not know how to help her and that you might get in over your head. And from listening to everything else you have said about this situation, I think you might just get in over your head.

I think the take away from this for you is that you are not alone in how you have unmet needs. You can see this other girl, and thats not a bad thing, because you are like this girl and there are others that are just like you and just like her that struggle. What you need to do is recognize the empathy and look into first learning about how to heal yourself and finally take the time to actually heal your own hurts, and when you do that, you will be better able to reach out and actually help someone else like this other challenged individual. There is a healing that does take place when empathizing and helping others. There is gratification that can happen from that too, and that is what encourages individuals to become therapists and social workers and individuals that quietly make a difference in the lives of others.

You have talked about suicide in this thread too. That desire is because you have hurts and unmet needs yourself and you have it figured out that if you don't find a way to fill that need and heal that hurt that you will give up and go off by yourself somehow and give up. I think that you should consider this situation you are experiencing on a different level. The empathy you have can actually turn into something postive, productive and rewarding. When that happens in a human being the toughts of suicide dimish and eventually go away. Empathy can be a bridge that helps a person from suffering to over coming and helping others do the same. But you cannot develop this empathy until you get the help to learn how to self heal that hurt in yourself that is causing you to empathize with this other person.

As far as the question you have of having a sexual attraction? Well, that depends on your history and what sex has meant to you. Sometimes individuals who have needs might try to fill those needs with sexual encounters. There is a confusion of trying to fill a nurturing need with sex and that doesn't work.

Now I have not read your history, but I do know that Borderline Personality Disorder tends to develop in individuals that were neglected and did not have the nurturing they needed and deserved from a parent. It could be from one parent or from both. Well, children do not know what to do with the stress that comes from that so often they develop other ways of filling that need. This is never the child's fault, never means they were unlovable or bad either. This is something that takes place because the parent themself is challenged and doesn't have the security in themself let alone raise and nurture a child.

I think the "interest" and "empathy" you have is a good thing sinking. It's something you can actually develop and build on. You have to explore this in yourself though and do some healing and learning and then you will have more to offer someone like this other individual. If you decide to get help for yourself and slowly gain skills so you can empathize and contribute? As I mentioned, this dance around with suicide will go away.
This is what is missed and unfortunately leads one to go without and think more about giving up and it should not have to be that way, it really is preventable.