My Dad and I didn't get along when I was a kid, and after a particularly nasty fight, I packed my bags and moved out at 18.

Fortunately, I had a great place to go...my high school sweetheart, had very forward thinking and liberal minded parents. They took me in to the house, and while no such demand was made of me, I took a room downstairs away from them and their daughter.

Within a couple weeks, normal teenager urges took effect, and I began sneaking upstairs and sleeping with my gal. One morning, her mom opened the door - didn't see anything "going on", other than the two of us in bed together.

Her response: "Would you two like some breakfast?"

I've never forgotten that moment. She showed incredible restraint and maturity, even though we as kids, weren't returning the favor. More than 30 years later, I'm married to that gal, and have a great relationship with my in-laws.

While it's certainly your prerogative as to what happens under your roof, my advice - ignore it, and/or embrace it. Your kid is 20 years old, and beyond effective parenting. You've done your job, instilled your values, and hopefully he's made you proud. Accept him and his "friend" with open arms, and be glad he feels so welcome in his parents' house.