Complicated story needs advise

[Samal]

Hi all,

My girlfriend (for 13 months) got the man she never knew she wished for, and we have grown closer and closer all the time. The is just that she has had a small doubt if this is for her and if she actually is the long term relationship type (eventhough she looks up to it and admires it). Secondly, she talked to someone three days ago who simply asked 'is this what your heart wants?'. Intellectually she says absolutely yes, but this make her try to follow this feeling for once.
Thirdly, she has birthday today, the party is tomorrow and I'm the one who helps her (I actually wanted to give her the best birthday possible). She made up her mind regarding the break up two days ago and asked if it could happen on Sunday. As I saw the potential of her changing her mind, I said ok. As I want her to feel that she misses me and to realize what she's about to do, I don't know if I should have said no rather than ok.
Lastly (this is the complicated bit), she has three young and pretty much fatherless siblings (6, 7 and 12) whom I have grown close to and they see me as a father role (they are obviously desperate for it). As they mean the world to her, should I keep seeing and loving them, and be 'the father role who remained with them', or should I make it a package that is 100% attached to our relationship? She doesn't get it when I say I feel it's unjust that she wants me to keep visiting her siblings while she just goes on and will eventually sleep with other guys and perhaps get a new boyfriend. I just can't cope with the thought of her having sex with another guy and that makes me retreat from staying in contact with her family (who desperately want me to stay in contact and to visit them).

So, to sum up my questions:
Should I keep seeing and loving her siblings and give them a stable father role? Is it more likely that she will see what a "stupid decision" she has made and come back, if I nurture her deepest concern (that her siblings get the best)?
Should I give her the best birthday I can? Or will this make it easier for her to break up and not want me back?
Should I wait until Sunday and be 'a boyfriend' to her, or should I say we can't go on like this until Sunday and end it today on her birthday as we will spend the day together?
I just us to carry on with the relationship, either now or after she has been alone for some time (1 month to 2 years?). How can I act the best in this regard?

Thanks for reading my long complicated story. Hope to get more clever and tackle it the wisest.

S

[Stay 2gether]

well 1st off congratulations for being there for the children when their own father is not in there lives! i think maybe it will be best for you to back off seeing how she has expressed that she wants to move on i dont want you to be there taking care of the children but getting your heart broken in the process i know it mite hurt but i think it may be the best for you and the children now not saying if you see them out and about you cant interact with them but that should be just about it. I think rather her bday is coming or not you should be honest and let her know how you feel about you alls relationship maybe she will understand and at least try to compromise to make things better if not you need to move on buddy enjoy your day

[Hooo!]

This is a doublethread.
see here http://www.loveforum.net/love-advice-forum/99869-complicated-story-advise.html