Quit feeling guilty. Your feeling guilty about this whole thing, and your son is wiggling into your weakest spot. Stand up, be the mom, keep up the discipline. No, he doesn't get to go where it may be 'more fun'. You have rules and things that occur at your house, that he must abide by. At 4, they like to challenge these rules anyway, just to see exactly how concrete they are. He's normal. He doen't dislike you. Your his mother. Talk him through his frustrations.
If you do anything, have a thorough discussion w/his father concerning this issue. You both want the best for your little man, and consistency in his life will keep him less confused. For instance, he should not be able to jump on the furniture at Dad's house, if you have a rule to respect the furniture. You will have to communicate w/the dad in order to do this much smoother.
You might want to find out if Dad is having alot of fun wiht your child, leaving out discipline. too many times, the mommy looks like the bad guy b/c you have to lay down the law. I was a child of divorce and my mom had custody of me- she was in charge of all the heavy duty stuff and my dad was there to provide entertainment on a sunday afternoon. gee, who would i rather be with? :) kids dont understand that whoever is the main provider will be the one with most of the responsibilty- and not the one who is most fun.
Hey there...I'm afraid that I don't have an answer for you but I just wanted to chime in here. I am also divorced and the boys eat out with their dad once a week and then spend every other weekend with him. It seems that my 6 year old is always asking when he can go back to his Dad's. He doesn't act unhappy at home or act out but when he repeatedly asks when he can go back it really gets to me....I don't see him as being old enough to make this decision and also I don't believe that his Dad can provide a better environment but I am also unsure how I should respond to my child.