hi my partners ex limits the time we can have my partners son too, this is because she dont like me even though we have been together 5 years. it has taken this long to finally get things sorted and we know have him every other weekend and can take him away in this country one week a year, not alot but better than nothing. my friend has this 12 week thing too and i believe it is to check on things like, the father turns up when he says he will, brings him back when he says he will, feeds and cares for him in the right way, and most importantly that the child is happy. they may not allow him to have him overnight untill he has his own house/flat and they what they think is a stable home for the child to stay. it can be such a long process especialy if the mother is arguin about it. it took us 5 years. i hope it is not that long for you and that they can sort it out. they may agree on him having his son every saturday or something similar untill he has a place to call home and then this may change to every weekend or other weekend.
does your partner pay maintanance for his child cause if he dont that will go against him straight away.