If a man and a woman who both love Christ are together, they would also both be vigilant about what can lead to temptations.
One man and woman may not be able to be alone together because if they are honest, one or both of them would not be strong enough to say "no" to the other if the other was weak and wanting to give in to what their flesh may desire.
So because they love Jesus they avoid that sort of situation if they are vigilant.
Another man and woman may be just fine being alone and playing games or having long discussions.
Though if they were to be more intimate and maybe try to lay together to watch something or maybe kiss, one or both of them may be tempted. If you or the other would be tempted to go too far it really is selfish to put them (or yourself) in that spot and, then it becomes a bad thing. (don't allow yourself to go too far in thought, word or deed if you want to avoid temptations)
Also if neither of you are able to say no or neither of you are aware of your personal limits and boundries, pray about it.
Be honest with yourself and the other. Take it to God, and don't play with fire. Better safe than sorry and it will all be that much more precious in marriage.