Viewers have seen the pair cheating on their respective partners Tony and Jacqui over the past few weeks, but in upcoming episodes Cindy considers ending the fling as the guilt becomes too much.
When Tony buys the Atwell's gym next week, Cindy sees that he is trying to provide a stable future for the pair of them, so she tells Rhys that their affair is over. But will she be able to resist temptation?
Digital Spy recently caught up with Stephanie Waring, who plays Cindy, to hear her thoughts on the ongoing plotline.
What has the Cindy and Rhys storyline been like to film?
"I've really enjoyed this storyline, because there are a lot of twists and turns coming up in it that I don't think the audience are going to expect. It's not going to just be your straightforward affair - there's lots of stuff on the way, and how it develops is going to be very surprising.
"I'd love people to invest a little bit in Cindy and Rhys. I've seen on the forums that people have said, 'Oh no, you can't break up two great couples!', but at the moment the fans have no idea where it's going. I hope they're going to enjoy it when they see it for themselves."
Is it nice to get your first long-running storyline in a while?
"Definitely. Last year was about introducing a younger group of characters, but this next year we'll revisit the families and the characters who have been on Hollyoaks for a long time, and see how everyone interacts together.
"I'm really excited to be involved in this current storyline, and I think it's some of the best stuff that I've done since I've been at Hollyoaks. I think the audience will agree with that when they see how it develops."
Why has Cindy's attention been drawn away from Tony?
"Well, Cindy is like a child and Rhys is like a shiny new toy to her. She does love Tony, as he's her staple and they know each other inside and out. Tony is Cindy's comfort zone and whenever things go wrong, she goes back to him. Tony has always been there for Cindy and he's put up with her for so long.
"With Rhys, he's just a bit of excitement - they're very alike and they both want the same thing at this current time. I think it's a believable storyline for a character like Cindy because she goes through men for fun and if she wants something, she goes for it."
Cindy seems to be feeling more guilty than Rhys, doesn't she?
"Yeah, you would expect Cindy to be the one who's all for the affair and for Rhys to be the guilty one, but in fact it's the other way around. Cindy is not sure if she's doing the right thing, because she doesn't want to hurt Tony.
"I'm not sure I'd go as far to say that Cindy is completely head over heels in love with Tony, but she knows that he's the right choice to make for her in terms of a future relationship. She doesn't really see it going anywhere with Rhys, as it's just a bit of fun.
"When Cindy sees Tony doing various good things because he's such a good man, she does stop and think, 'What am I doing?' But like I say, she's like a child so when he's not giving her attention, she'll run back to Rhys."
Why does Cindy react so badly when Tony proposes next week?
"Because soon after Tony proposes, he lets it slip that he thinks she's pregnant. Tony admits that it's pretty much the only reason why he's popped the question, and Cindy is really angry at that. It's not the fact that he's proposed, but just that he's only doing it because he thinks she's pregnant. So she's not happy at all and storms out."
How does Cindy feel when Tony later buys the gym?
"I think she thinks he's a little bit bonkers, but she supports him and she's pleased that he's done something so grown-up and responsible. Tony is basically providing her with security and that's appealing to her, as she's always wanted a man who's going to provide her with all of the things that she can't do for herself.
"Afterwards, Cindy decides that the affair is over and she's going to stay with Tony, but you'll have to wait and see whether she can resist temptation again."
Is there a part of Cindy that wants to get back at Jacqui with this affair?
"No, I don't think that is her motivation as Cindy isn't that callous. She wouldn't have an affair with Jacqui's husband because she doesn't like her, it's just an unfortunate situation. I think those two could actually be friends at some point, but at the moment they just rub each other up the wrong way.
"Cindy and Jacqui have never had any kind of friendship, but I think they're quite similar. They're both strong women and they're both out for what they can get."
Could Cindy have any involvement in Darren's troubled times at the moment?
"I'd love her to. Even if Cindy and Darren weren't a couple, I think it'd be great to see more from them as a pair. I think they've got great chemistry whether it's as a couple or as friends, and I'd love the writers to come up with a storyline for us both so we could work together again. I love working with Ashley [Taylor Dawson] and I do miss sharing scenes with him."
Bryan Kirkwood was the one who brought Cindy back in 2008, and now he's back as executive producer. How does it feel to have him back in the building?
"I absolutely love Bryan. He knows Hollyoaks so well and he knows the inside out of every single character. With the newer characters, I think he'll make them his own and put his own stamp on them. I'm so excited for the next year on Hollyoaks."
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Hollyoaks airs weeknights at 6.30pm on Channel 4, with first look screenings at 7pm on E4.