What is intriguing to me is that you say you don't want to end things because of the good memories together and can't stand the fact of thinking about her and someone else together. Understandable, however this shouldn't be the reason to stay with someone, in my opinion it sounds like you're just not ready to be alone yet, so you're trying to make it work so the relationship doesn't fall apart.
I can see where you're coming from wanting more concrete like plans, but I can also see where your GF is coming from as well. It could be that she doesn't want to make any solid plans because what happens if they don't pan out?
I've had this talk with my SO many times, explaining to him that we do have to take things day by day/week by week sometimes because if I see him putting up (for lack of a better word) requirements for our relationships future I get very anxious and worried, because then I wonder if things don't work out like he would like, how will he react? Will he blame me? Will he get really upset over it? Will I be able to lift him out of any funk if that happens? Etc.
People deal with planning for the future differently. LDR's just like in person relationships are a two way street, it can't all be about what you would like all the time or what your SO wants, you find a happy medium.
You need to find that with your SO first, and learn how she copes with situations that don't work out. I'm not saying "Oh well she says she's fine, so everything is cool." No. Really get her to open up to you and you do the same with her. I agree with the comment above me, visiting for a week or 10 days is no substitute for how your relationship will be like when living together, it is true that those short visits are vacation mode, and you don't really get a chance to settle in and get comfortable with each other.
I'd say communicate with your GF more, listen to what she has to say, reassure her that until you understand what her apprehensions are, you won't make any definitive plans just yet. She may have ideas or wishes you have no clue about and her neither, but really take the time our to talk.
Just my two cents.