They met at a mutual friends' (Mark & Kaylee) house. Priska was visiting the friends at their house on the Air Force base in Washington and Marlon who was still active in the military then, happened to be spending his evening at the same friends' house. Voila! And no, there was apparently no spark between both sides (until Marlon confessed later on to Priska that he thought she was cute).
They have booked a reservation at The Perch, DTLA on this night for Priska's birthday on the 19th. Priska said she didn't expect anything at this point because she said this would be a classic proposal case and Marlon probably wouldn't go this route. Sure enough, nothing happened during the dinner at The Perch. They drove home, took a walk around the neighborhood to digest some food and returned home. Once inside, Marlon didn't waste anytime and got down to one knee and popped the question. Marlon apparently had planned to pop the question at the restaurant or during their walk (to go get ice cream a block away) but waited until they got home because the situation at The Perch was not suitable, the ice cream shop had closed and the night was getting chilly. But... it ended up being the best proposal ever in their most intimate and comfortable space.