The pair became engaged last month, but in next week's episodes, viewers will see Steph declaring that she cannot marry Gilly unless he accepts the reality of her illness, leaving their future uncertain.
Steph was diagnosed with cervical cancer in June and her portrayer Carley Stenson is due to bow out of the Channel 4 show towards the end of the year.
Speaking to Inside Soap about the storyline, Quinlan commented: "I think Gilly's really gutted that he didn't get together with Steph sooner - he wasted so much time with Cheryl and Jem, when really he was in love with her.
"I'd love to see them finally tie the knot before Carley leaves. Imagine how tear-jerking those vows would be - 'Till death us do part' and all of that. I'm welling up thinking about it!"
Meanwhile, asked how viewers have reacted to Steph's plot, he replied: "People are upset about what's happening to her - in fact, I was sitting watching Hollyoaks with my mum the other day and she started crying, bless her! But the feedback I've had so far from viewers has been just brilliant."
Stenson is planning to pursue a career in musical theatre after she makes her Hollyoaks departure.