My Mom's Ex-fiance's Daughter

The alternate reality version of myself is in town. Sometimes she even stays with me. I really like her, and I really dislike her, all at once. She's a sensitive optimist, whereas I'm a "rolling stone" pessimist. She never shows up to sleep on the couch when she says she will, and she isn't responsible enough to keep her cushy job, and she's couchsurfing everywhere. She drinks too much, and gets people to buy food for her. I made the mistake of introducing her to my friends and now she's moving in with one of them.

Jay says she's just like me, and watching us argue is like watching me argue with myself. I like to think I'll be more responsible 5 years from now (when I'll be her age), but I don't know. She freaks me out. I feel like she's taking advantage of me by not showing up when she says she will- something I've told her really bothers me. I don't like her stomping in at 4 a.m., but if I wake up and it turns out she never showed up, then I worry. And I mean, what if a friend wants to pass out on the couch (as happened over mardi gras) and I say no, because she's supposed to be here? And she stomps into me and Jay's rooms without knocking or asking.

Still, I can't deny the affection that unfurls in my chest while talking to her, or the joy I feel, thinking I have something sort of (but not-really) like family in town.