Viewers have watched as Gary's feelings for the surrogate mother to his and Izzy's baby grew over the past few months.
Actor Mikey North explains: "Izzy is not able to carry a baby full term, so Tina is having to carry it for them in exchange for quite a lot of money from (Izzy's dad) Owen, so it's not a situation that you find yourself in every day."
Sneak peek footage shows it all gets too much for the former soldier and he decides to show Tina how he feels about her.
"Gary can't wait to be a dad; he's looking forward to his baby being born. But his feelings are starting to get a bit mixed towards Tina, whose carrying the baby," he said.
He just goes for it and goes in for a kiss, and she hits the roof.
"Things come to a head on the day of the reunion with his army friends. They've been talking about Tina at this reunion; they've been mocking him saying that he fancies her. He's denied it and he comes back to the Street a little bit drunk and decides to call round and see her."
After being rejected, a guilt-ridden Gary tries to make amends by focusing his attentions on the unsuspecting Izzy.
But, as Mikey explains, the incident won't be as easy to forget as he had hoped.
"Tina confides in (ex-boyfriend) Tommy, much to Gary's dismay, and I think he's more worried that he is going to say something rather than Tina," reveals Mikey.
"Tommy still has feelings for Tina, so obviously when he finds out, he's not happy. I'm sure he's out to get revenge on Gary for them breaking up in the first place.
"The big question is will Tommy keep it to himself, which obviously no-one knows.
"It's a case of watch this space and see what happens with Tommy and Gary."
Coronation Street is on UTV on Monday, Wednesday and Friday from 7.30pm.