The Demon Lied. Go Figure.
Well, Dave FoO is a smart guy, reads all the posts, understands the general situation here. So to get to the doors, he enters the room, steps over the runes, and gets about halfway before the demon takes his five attacks. Three hits, for 15-3=12 hp dmg.
Start of round one, the demon attacks again. Two hits and a double damage, for 23 more. Dave FoO, you're down to 4 hp.
The demon's AC, by the way, is -4. So Moth, I think your 17, while respectable, is actually a miss, sorry to say. Don't forget that your sword is +1, your STR is 17 (giving you a +1 to hit/+1 damage), and getting 3rd level fighter gives you another weapon proficiency.
We're not fucking around here, obviously. Good luck, you'll need it.