Lisa Goldstein and Lee Norris Lisa Goldstein and Lee Norris

How do you tell your boyfriend he's gotten fat? That's a question One Tree Hill's Millie will face on Wednesday's episode.

"Mouth has no idea what's wrong," Lisa Goldstein tells "He hasn't taken a good look at himself in the mirror and Millie is struggling with how to tell him."

Tragedy, Transformation and Troubled Couples: What to expect from One Tree Hill's last season

Although last week's episode lightly addressed the plotline, both Goldstein and Lee Norris say the problem will be treated more seriously. "Obviously he's unhappy; otherwise, he wouldn't be eating everything he sees," Goldstein says. "Millie gets a little insensitive, but Mouth needs a push in the right direction. At the heart of it, Millie is concerned with his well-being, not how he looks."

The couple have had their share of ups and downs and hit a significant rough patch when Millie began using drugs. But Goldstein says this latest problem won't be the end for them, either. "They've made it to a point in their relationship where they can get through conflict together and become stronger at the end of it and it's what they're good at now," she says. "At the end of this season, they're really happy with where they're at and they'll probably continue on the path you'll see form."

And speaking of the season's end, Goldstein adds: "I am most excited about the season finale, especially the last few moments of it. Everything is wrapped up like a bow like the fans would want it to be."

One Tree Hill airs Wednesdays at 8/7c on The CW.