<human>: To start, I obviously had to have a throwaway on this one. 
I'll make this as quick as possible:
I live with my fiancee, luckily she doesn't come to this subreddit. We've been together a couple of years. Social pressure forced me to become engaged to her. She's a slob, disorganized, can never settle on what she wants to do in life, is notorious for being late to things (all pet peeves of mine) and worst, she only seems to be getting worse. When we met, and even in the beginning of our relationship, she seemed bright, focused on academics, and what she wanted out of life, now she just floats through everything.
I've been miserable these past few months, unknowing what to do.
Then an old friend started working where I do.
Oddly enough, my friend has had history with my fiancee, as when she (my coworker) was younger, she attempted to seduce my fiancee's then-boyfriend. 
Well, my friend/coworker is having relationship issues (isn't technically in a relationship, it's complicated), and I have been offering advice. We've been talking, we went on a 'date' the other night, been spending hours together these past few nights. We know our limits, and tell ourselves we can't cross them. We're both machiavellian, we've used others in the past, and we're okay with the fact we might be using one another. I offer her an escape from monotony, and she offers excitement in a chronically depressed individual's life (that being me)

What the hell should I do, reddit? I, for some reason, don't feel guilty. My friend's scent has helped comfort me to sleep, her voice relaxes me, and I know I can't have her as a lover, ---only a companion. I'm oddly okay with this, it's almost something to strive for, and should I fail, I will have known my limits in the first place.

I don't know what to do. My fiancee is going to be gone until the 30th, and the girl is coming to hang out with me tomorrow, as well as later in the week.

Can you provide a brief rundown of the text in within 3 sentences?
<bot>: I'm stuck between a relationship that is tearing me apart, and a girl that might use me and throw me away (which I'm completely fine with)