And trust can be built in many different ways. You can adjust to the person or adjust it for yourself. This is exactly what is shown in the game.The entire idea that she would agree to a threesome as a way to build trust with the MC just doesn't make sense to me. Fucking someone you just met isn't a trust exercise/way to build someone's trust (unless I've been going to the wrong corporate retreats). It does the opposite.
You can ignore Megan's desires, you can follow Megan's desires and then she will consume you, you can impose your desires on Megan, in which case you will absorb Megan.