They like and understand each other. They help and support each other.
They like the comfort of it. And because they want to I suppose.

Because they like cuddles,nowt wrong with that.

Mario has been good for Andrew, building up his confidence and becoming a mentor in a way, which is nice to see!

Cuddles and spoonage. It's nice.

Why not I suppose.

I don't quite see it like that. I think Mario has been using Andrew for his own ends. I wish there was more time to go and Andrew stop sharing a bed and see how Mario falls into his usual depressive self.

I certainly don't think Mario has used Andrew.

They've just "got along" well; simple as that.
I think their relationship and support has been entirely mutual.
I certainly don't see why they they should use separate beds.
That option was clearly available, so I assume that neither of them wished to sleep alone.

Because they want to.
If Mario was not a gay man would the question be asked .

well yeah actually it would

I totally agree.  Mario might have good intentions but it's the patronising way he's going about it I don't like.

Well they are clearly happy to share. 

Don't underestimate Andrew, if he didn't trust Mario 100% he'd soon move away.