Because it's change.
Most people feel a bit odd when changes occur.
You're used to there being a male presence around - Neil from a young age, then Robbie when you broek up with Neil.
It'll take time to get used to but the point is you don't need the guys.
It's like suddenly realising you don't need half the stuff in your handbag, and that you can fit everything you do need into a small sexy bag instead.
It feels odd because it's small and lightweight - you wonder how you'll cope without all the stuff you took out.
In reality it was jusst baggage - you never needed it - it was just there and now it's gone.
Give it time and soon the new lightweight handbag becomes the norm and you wonder how you managed to lug all the junk around for so long.
Because he's feeling a bit hurt.
So what - he'll get over it.