Donna! Oh how I've missed you.
It was brilliant and I can't think of anything else to say...and I've tried.

“Is it serious, Jack?”
The question seemed to shake the other man from his thoughts.
“Serious? We’ve only been seeing each other for a couple of months, Doc.” He continued to stare across the room.
“But I think you’re serious.” Jack whipped his head round. “C’mon, Jack. I know you- you haven’t even flirted with anyone tonight!”
Jack slowly nodded his head in realisation. “...OK... I want this to work out. But... Ianto... he’s straight. I keep thinking he’s gonna wake up one morning and he’s gonna realise he’s made some kind of mistake. And you can’t fail to have noticed that he’s younger than me...”
“Mistake? I saw the way he looked at you. Are you blind? He’s as besotted as you are!”
“Oh... Do you think?”
“Gods- you are blind!”
Jack laughed, back to his old self. “I hope so, Doc, I hope so. I guess we’ll see.”

Although I really loved this bit. There's just something about insecure!Jack.