So which is better for romance, lust or pure path?
Both. One thing we've told players from the beginning (it's also mentioned in the tutorial a bit) is that on your "main" playthroughs, the game is best played without trying to manipulate stats or variables too much -- ideally you should select the choices that make sense to you or that feel right rather than trying to strictly adhere to any one path. If you're purely looking for romance from a story perspective and don't care about "content" as much, Purity. If you're purely looking for content and don't care about story-driven romance, Lust.
The most balanced path from a romance & content perspective is a mixture of both Purity and Lust.
Recently added this to the dev notes for more clarity... hope it helps!
It's the scene where you go to the woods with Ali.
This is indeed a bug/will not be the case in v0.4 Full. That said, if you or others don't feel like replaying the chapter (continuing to new content from saves made in "beta" is never recommended, but you won't
have to restart)... there are many opportunities to switch the path you're on with the girls throughout the game.
Also as an aside because it's been mentioned a couple of times... the non-beta version of 0.4 uses Ren'Py 7.5.3.