Conspiracy Theory of the day: Ashley never had a boyfriend in London.

Season 4 closer, she went to London to get away from Craig. He was batshit crazy at the time. She couldn't stay in Toronto and be broken up with him. Because look at how Craig acts when someone tells him no. Always having to worry about what's going to set him off, or if he's on his meds today.

When she reappeared in the season 5 closer, wearing the Ridiculous Hat of Deceit, she said something really vague about her London relationship going well, then bad then ending. It never happened. She needed a reason to stay past the summer. Craig is too pushy and hyper-fixated on what he wants when off his meds. Also he's too charming and too handsome, she wouldn't have been able to stay away from him.
Summer wasn't enough time. She couldn't come back until she and Craig had both moved on to something else. She wasn't really all that icked to hear he was back with manny.