I seem to remember reading that all they need to disfellowship you is for you to spend a night with someone of the opposite sex in the same room/building. If it's important not to be DF'ed for you, don't take risks you don't have to.
EVERYTHING depends on who you are. I knew a young man who spent MANY nights in the home of an older woman, she had 3 or 4 children.... He was spoken to by the elders on a number of occasions. Nothing ever happened to either of them. They got married about a year later and everyone was so 'happy' for them.