Suzie asked Tosh to her flat only because she was sick of hearing about Tosh in jail. To Suzie, Tosh's arrival sounded like "Boo hoo, I had a good job before I was blackmailed" and "UNIT prison was horrible" and "I can't make a sonic probe but this Doctor gets to carry one around the universe." Did she ever tell Suzie she met the Doctor once? Yes, Suzie knew.
Even calming Tosh's fears grated on Suzie's nerves. "No, it's not a violation of your probation if you come over to my flat for drinks."
That's how their drinking sessions began.
One time, the Blowfish and some Zygons made an alliance to terrify Cardiff. There was a lot of shooting of Blowfish, Zygons pretending to be Blowfish, humans, Suzie, and Tosh, and Zygons as Zygons. Tosh nearly shot Suzie. Suzie had to wave her hands and scream to prevent Tosh from shooting her. It wasn't Suzie's time to go, not just yet.
Tosh almost accidentally shooting Suzie scared both of them. It was enough for Suzie to suggest drinks at her place after the incident. Pilgrim and her grand plans had to wait. Suzie couldn't think straight after she nearly died.
Another time, to Suzie's surprise, Tosh showed up at Suzie's flat. "I know you're having sex with Owen," Tosh said.
"Yeah, I'm fucking him," Suzie said. "I don't love him. I don't give a shit about him. So what's the problem?"
(Suzie had no idea Tosh liked Owen. She'd die twice never knowing about Tosh's feelings.)
Tosh let the matter go. "Can I come in and have a drink with you?"
Suzie regretted inviting Tosh for drinks every so often. She was about to go to a Pilgrim meeting. "Sure," Suzie said. She had to keep up appearances for Torchwood.
It started out with one beer between them, shortly after Tosh joined Torchwood.
Then Tosh learned about all the horrible things coming out of the Rift as well as the things lurking about in Cardiff and other areas in Wales. Tosh never told Jack to keep up appearances.
Suzie was already jaded by the hazards of Torchwood. She was more worried about her grand plan failing. Maybe something wouldn't go to plan. Maybe she would never live again instead of being immortal like that bastard Jack Harkness.
Over time, "two beers" became "one six-pack" to drink away the fears.
"I don't want to die working for Torchwood," Tosh said one day, drunk on Suzie's living room floor. "I want to go back home and see my mum again."
Suzie was beside her. "I think Torchwood is driving me crazy. There's formal procedures for everything. We're always running around chasing things and putting them in the archives or killing them. This life isn't going to end unless the government ends Torchwood."
Suzie threw her right hand to the ground. Tosh grabbed it.
It was a shame, really. If Suzie met Tosh earlier, she'd be the perfect girlfriend Suzie's always wanted.