Lindsey ending is the default ending and Aubrey+Riley ending is triggered only if you previously hooked up with Aubrey and Riley.
Though at least V13 scene with Riley doesn't count. If you're only interested in seeing the Lindsey ending, you can use a console command (open the console with Shift+O) to jump to the scene:
Standard disclaimer: you should never save the game after an arbitrary jump unless you know what you're doing.
Well, based on my analysis, I asserted that you can either see the lewd scene with Chloe or ferris wheel date with Lindsey. The V13 ending doesn't depend on your relationship with Chloe in any way.
If you're saying that you saw the lewd scene with Chloe in the hotel room AND went with Lindsey, I don't understand how that is possible. I'm looking at the code (game/v13/scene39a.rpy) and all I see is this branch in the pool scene with Ryan:
Code:
if chloegf:
jump v13s40
else:
jump v13s41
In other words, if Chloe is your girlfriend – that is, she accepted when you asked that in London car dealership – you will jump to scene 40 (entitled "Chloe Sex Free Roam"). If not, you will jump to scene 41 (entitled "Ferris Wheel date with Lindsey").
Update per 13.1.1 patch: I said "Though at least V13 scene with Riley doesn't count." That was true then, but as of 13.1.1 patch, if you take Riley's offer, you are considered to be in "relationship" with Riley. So it does count.