A better way to interpret that verse is to "avoid evil every time it appears", otherwise you would have to condemn Jesus for violating that principle throughout His incarnate ministry (healing on the Sabbath, dining with tax gatherers, eating and drinking wine, touching sinners and allowing them to touch him, allowing his disciples to "harvest grain" on the Sabbath, overturning the trading tables on the Temple grounds, etc).
Certainly we need to do our best not to give people the wrong impression, but others are going to think what they want to think and we can't be held responsible for that.
Now to the issue raised in the original post, I think it is unwise for unmarried men and women (especially if they have a romantic relationship) to sleep in such close quarters. It is not necessarily sinful, but we also need to understand human weakness and the potential consequences of our actions.
Back when I was dating my wife a number of years back, we went to visit her aunt and uncle out of town. When we were bringing our bags in from the car, her aunt showed us the guest room where she intended the two of us to stay. Between the two of us, we stammered back-and-forth until I finally said (as graciously and humbly as possible) that we had established some boundaries when we first started dating, and sharing a bed for the night was outside of those boundaries. I ended up sleeping on a bed intended for a little girl (imagine a 6'05" 240 lb guy, built like a defensive lineman sleeping in a fetal position on a pink bed).