Check to see if you responded but nothing. We are trying to help you get control of these issues and will be glad to add other suggestions. I won't add any more if there is no response.
I can hear your frustration in you post and understand completely. Not easy to answer briefly and I have a few questions.
Is the dog neutered? If not, neutering him (no matter his age) may or may NOT help the problem.
Not to get personal, but when did the boyfriend come into your life and start staying over?
What breed is your dog? If he is a small or toy breed, they can be very hard to train not to mark things in the house.
Are you using something with an enzyme in it to launder? If not, you can use a vinegar rinse.
Rubbing his nose in the area he marked will not have any effect. You really should only correct the bad behavior when you catch him in the act with a firm *NO!!!* and take him immediately outside to an acceptable area he uses whether he has peed already or not.
Is he being left alone more then usual? Does he have free roam of the house when you aren't there? Is he only doing this when you are not at home? If so, it may be an anxiety issue.
Does he sleep on your bed with or without you? If so, don't let him as he is then on the same *level* as you and you loose pack leader status. Does that make sense? LOL :-)
If you can answer some of these questions, perhaps we can discuss this a bit further.
If I had to wash sheets 9 times in one week, I'd probably call Animal Control. Kidding, just kidding. Now, take a deep breath.................
Six is not old for any breed of dog, it's just into middle age. If he's been doing it for the past 2 years then he started it when he was four, and four is still considered young.
It does, indeed, appear that it's some sort of marking behavior. Is your dog neutered? If not, then it MAY help to neuter him, but unfortunately once a behavior is this deep-seated, even neutering won't help it. The only way to keep him from doing it is going to be to make sure he has no access at all to your room. If you or anyone else go into your room you're going to have to make sure he's not behind you. If you keep the door shut, unless he's a magician, he won't be able to get into your room unless someone else lets him in.
At this point, he has probably marked the area so much that washing the sheets isn't enough to remove his scent because some of his scent is now on the actual mattress and box spring. It might be that to totally stop the behavior you are going to have to completely change your bedding, right down to the mattress and box spring.
In any case, rubbing his nose in it is an old-time training thing that has been proven to have absolutely no merit whatsoever. He will learn nothing from it and will just continue to repeat the behavior until all traces of any scent he leaves behind have been removed, and ideally, the reason for him wanting to mark in the first place has been removed. The bad thing is it may be your boyfriend that is causing him to mark, he feels threatened by the presence of another male in what he thinks of as "his" room, so for that reason, the only sure way to get him to stop marking is to completely ban him from your room.
Ghilly