[trancehead]

she just ended last relationship
was single and ready to mingle . and found you
got to know you, and maybe knows you too well now

now she has a shiny new toy in front of her.
she wants to know this too now

lets try and be objective here. was the new boy an upgrade? if massively yes (looks, wealth, social status) . or if not an upgrade, she just wants the shiney new toy for that new novelty factor

this is just human/womenly nature.
just distance yourself from her. that may be the best thing to do. if she come crawling back, then hopefully you know how to take control of the situation moving forward. you win

if she doesnt come crawling back, you still win. plenty of girls out there.

..and your question about being used. do not frame this on yourself. it just sounds like youve been victimized (not only to others, but to your own conciousness as well). you are only a victim if you frame yourself to be one. but no, that is not the proactive way to approach this situation