We got two new cats about a month ago. One is a 1 year old spayed female, the other is a neutered male of about 5/6 months. We got them from a rescue centre, and the staff their think they might be mother and son. They were never allowed out in their previous home and I don't think they've ever been separated, they are very close and affectionate with each other.
However, we've started letting them out into the garden, under supervision at first and now while one of us is around. Boycat likes to scamper around - not too far from the back door, but he's happy to explore and climb and pounce etc. Girlcat was a bit more timid but lately she's been happy to wander off a bit further.
The problem is when Boycat suddenly realises Girlcat is out of sight. He goes BONKERS - scampering about and yowling and coming to the back door and yowling some more, and if I let him in he is frantic, pacing around obviously looking for Girlcat and shouting at me as if to ask where she is 
, and sort of throwing himself on the floor (including in the food/water bowls). If he notices the biscuit bowl, he'll calm down and nibble at those for a bit, and then it all starts up again until Girlcat returns. He seems really, really attached to her. I don't think she's as fussed, if he's shrieking round the garden she won't necessarily come back to him straight away.
So - is there anything I can do to get Boycat to, well, man up? He's about 6 months old, so still quite kittenish but I would have thought he'd be up for doing his own thing by now instead of being a complete mummy's boy. Should I just give it time? Or should I get him into therapy?
thanks for any advice!