L.C.
Your ex gets to be the "Disneyland Dad". Your son gets to go there and be treated. There probably isn't alot of discipline or rules because he doesn't want to spend the time with him in a negative way. They probably also do special things since it's only every other weekend. I have gone through this for the last 18 years, and especially the last 10. My 2 older sons are from a previous marriage and for the first 10 and 8 years of their lives, even though their dad lived no more than 20 minutes and sometimes as close as 7 minutes away, he was never there on a regular basis. He missed birthdays and holidays. He was very inconsistent but when he was there is was like spending two days at the circus. He lavished things on them. But then all the other times the boys would fall asleep on the sofa with their coats on and their bags next to them and he would never show up.
I got married to a man who loved us enough to make all of us family. At first it made no difference other than to make my ex seem like a spoiled little boy who was getting his favorite toys taken away. Then he met a woman who made it a condition for being with her that he be a better more consistent father. All of a sudden Disneyland Dad was on the move. In the meantime, my husband was the real father. He took care of them when they were sick, coached their little league, played in the yard, helped with homework and gave them guidelines and guidance. Their biological father never did that, but if he got up and tied his shoes he was a hero. It was hard a lot of the times. Parenting is thankless on the best days, but this was like being slapped in the face almost.
Things to consider are these: Even though he came in late and this is frustrating for you, it is so much better than your son suffereing the rejection he would feel if your ex had never stepped up. As good a dad as your husband is, it would not have covered for the fact that his biological father rejected him. The main reason he doesn't want to go home has nothing to do with how good a M. you are or how good a dad your husband is. It has everything to do with the fact that he is having fun and that he assumes that everyday would be like the weekends even though you know it wouldn't be. Little ones tend to romanitcize the part time parent and put them on a pedestal. The have ideas of what it would be like. It will be like this when he gets older too. "If I lived at my dad's I wouldn't have to (insert unsavory chore here)." The important things is that YOU know better.
Lastly be comforted in the fact that when he gets older and is better able to see the lay of the land he will KNOW who parented him, who loved him, played with him, taught him. Like the wash it all comes clean in the end. So just be patient with him and keep your head up. This time is just a season in a really long life. It gets better.
L.