There are indeed two endings. You need to have sex a certain number of times to fill up the bar to the key, so the hell door will unlock to let you into the final boss area, but if you have too many more scenes after that point, it will start flashing read, which does indeed get you the bad ending, where you get caught as your escaping and don't make it out with everyone else.
I have gotten both endings once, because I have only succeeded in killing the damn final boss twice, because the damn thing regenerates so fast, and you only have a split second to react and dodge while your punching it when it tries to grab you in various ways.
One of those times, was when I managed to glitch my positioning slightly, so I was to the right of the node that you hit to damage the boss, but far enough left, that I didn't get launched away to far wall, and just smacked it until it died. I've never managed to get into that position again, and only once, through luck and RNG managed to kill it normally. Any one with advice on killing it, would be much appreciated.