Ziplex
I am not a step-parent. I can only imagine how hard it is.
However, while you can choose to become a step-parent, the child gets no choice in the matter whatsoever. But that person can have a major impact on their lives. Therefore, it is essential that all the adults put the children's needs first and act in their best interests.
Needing space is normal and doesn't make you a bad person. Wanting time with your partner is also normal and it doesn't make you a bad person not spend every waking hour with your children.
I don't think wanting time with her husband/feeling knackered and frustrated is what's what's getting the OP a rough ride here. The way she writes about her DSS, as though he is an inconvenience she would like removed or some nosey/noisy lodger, is what she's getting a hard time over. Maybe she has just expressed herself poorly, but it does come across as very self-absorbed and selfish. I wonder how her DH feels about this situation?
This boy lives with his father and step-mother. It is his home every bit as much as it is the OPs DDs home, or her home for that matter. Yet the OP does not seem to see it this way- it's as though he's there on sufferance.
What is also coming across is that it is quite obvious that there is some difficulties between her DSS and his mother. But the OP seems totally oblivious to this fact, and is more absorbed in getting him out of the house so she and her partner can have more time as a couple.
If it really is as straightforward as his room is damp, then she should be asking her DH to have a word with the boy's mother about the state of his room. I wouldn't have thought anybody would have wanted a child she even vaguely cared about sleeping in a damp room though, far less be cross that he didn't really want to sleep in it and be fixated on persuading him to. Yet I would be wrong, because the OP thinks this is appropriate.
It may be a bit more serious than a damp bedroom that though. If the OP- or even better her DH- had bothered to try and find out why he doesn't want to go, and then attempted to address the problem (if that's possible), they may find he is willing to go to his mothers and they'll get their wish with a lot less fuss and upset. Also, they will have a happier, more settled teenage boy.
And if it's not something that can be easily sorted, then they are at least aware of a problem which is effecting their DS/DSS, and are able to support him. But no, the OP does not seem to have considered the possibility that there might be something troubling her DSS and seems more concerned about her problems.
Please don't misunderstand- I can understand that she wants to spend more time with her DH and believe that their relationship is also very important. It sounds like the OP does need more time to herself too.
However, her DSS is not to blame for this situation, but seems to bear the brunt of the OPs frustration which is not right or fair. The answer to the OPs problem is not treat her DSS as an inconvenient lodger in his own home, and ship him off to his mothers at the first opportunity despite the flagging up of a potential problem and ignoring his needs and wants.
It seems to me that the OP resents this boy for merely wanting to be in his own home. Her issue really is between her and her husband, and them making time for each other. It may take a bit more effort, and it may be easier if her DSS could be forced out of his home for their convenience- but it is not impossible.
And my question still stands- what's she going to do when her DD is a teenager and she has nowhere to ship her off to every other weekend?