I applied for my wife twice before we got married, and was rejected both times. I think the general consensus on the forum is that it does not impact PR in any way. Also, we explained clearly in the application that we we applied for TRV because we wanted to be together, and plus we had a reception event here in Canada that we booked hall and services for. We attached all of the documentation, including the rejection letter, our hall bookings etc. I don't think there is much to worry. Just being honest is good enough.