A bad thing?

So we have been trying to get M to sleep in his own bed, and he has been doing so well. He had slept in his bed for over a week. Well, B is gone on business. Monday night, M climbed into bed with me around 3 am. Last night, he wanted to sleep with me. I attempted several times to get him to back to his room with no avail. It got down into the 20s, and I worried a little bit about the temperatures, so M slept in our room last night. Now I am worried that he is transitioning back to our bed, and we will be fighting the same battle again when B is back in town.