Posh is in a constant state of exhaustion, overusing his mind making it difficult to sleep and hardly working his body is just going to lead to bags under his eyes. It could be said this is partially why he has a 'takes no bullshit' attitude and is rarely intimidated into bending (both mentally and physically).

Even someone threatening a physical fight can be dodged, outsmarted or beaten with magic rather than swinging a fist in his opinion. He's no idiot that allows stubbornness to get him killed though, if an actual beast comes his way he will run. 

Posh seems to be constantly tired due to his brother antics, and having insomnia doesn't help. He's not all cold and stone though, he's very witty and has a dark sense of humour some can appreciate. What's most surprising however is the easiest way to make him laugh is with some good ole slapstick humour, it's why despite his brother best efforts with puns, Socks is the one who can make him chuckle. 

When it comes to relationships Posh is more the type to be dragged into friendships by his brother Pish or Poppy. On his own, he can make some sort of truce when he's at least a bit sappy. Kinda like those friendships you have with people in class, you'll hang out with them at school but outside of it, they don't really exist. 

As for the romantic sort, he'd rather a classy lady to match him in his less than optimistic views since he seems to somehow be surrounded by sunshine. It can be romantic in a way that he'll feel obligated to follow it by the book, roses, candlelit dinner... more roses? He doesn't really know on his own. But he does feel responsibilities and obligations. If he's honest though he enjoys the physical side of it more. Again he's straight to the point and logical like that.