This whole thing is a BS sham, you are doing boyfriend/girlfriend things together which instantly blows the friends with benefits thing out the water.
now with that fixed in our minds lets roll...
You want a relationship with her--she is happy to carry on with this pseudo relationship and it sounds like you are the needy jeleous one.
You need to esablish if she is fking anyone else or dating other guys-- but dont bring it up in a needy desperate kind of way, tell her afterwards that you are getting offers but dont want to see anyone else as you enjoy being with her.

now ideally we have established that-- she isnt shagging any other guys and she isnt dating other guys. (if she is doing both then you are in a no-win situation)

I personally would then just be honest with her and say that-- you are both virtually a couple anyway and you would like to be exclusive with her and see what happens.

if she blows you off - then walk, its a gamble but you are in an unhealthy relationship emotionally for you--its turning you into a little needy jeleous bitch.

give her a couple of weeks of no contact other than maybe the odd small talk txt.
hopefully when she is starved of those coupley things you did together and she is in bed at night thinking-- she may just come round to you and give a relationship a try.

If not.. it IS for the best and you need to move on.