Michael Urie Michael Urie

When you find hot and heavy pictures of your fiancée with Derek Jeter, what do you do?

The logical answer might be to confront said fiancée. But if you're Partners' Joe (David Krumholtz), you tell your best friend Louis (Michael Urie) — as you've always done.

"That's just his instinct," Urie tells TVGuide.com. "They share everything with each other, and have for almost 30 years, so why not this?"

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For starters, there are new rules to play by following Joe's engagement to Ali (Sophia Bush). Also, Louis can't keep his mouth shut. And indeed, after Joe does show-and-tell with Ali's incriminating photo on Monday's episode (8:30/7:30c, CBS), Louis concocts a plan to play "Celebrity" with Jeter as one of the names to coax Ali into coming clean to Joe. But it all backfires when Louis' pop culture-illiterate boyfriend Wyatt (Brandon Routh) draws Jeter and can only muster up "he had hot desert sex with Ali" as his clue. (Check out the sneak peek below.)

"That was so much fun to shoot. It's just hilarious," Urie says. "You would think that if Louis was going to tell Wyatt, he'd let him in on the plan too."  

Naturally, Ali is upset — not so much with the fact that Joe went through her stuff in the first place, but that Joe automatically runs to Louis first and can't seem to keep a secret from him. "She's going to test him," Urie says. "It's hard for all of them now that they're engaged. [Louis and Joe] still have a bromance. But now it's Louis and Joe and Ali. There's still a lot of conflict that's ripe. ... Louis has always been the No. 1 person in Joe's life and now he's not supposed to be anymore."

But Joe spilling everything to Louis is only part of the problem. Louis, the "sh---stirrer," as Urie endearingly calls him, loves to meddle in his lifelong friend and business partner's life. That has yielded results both negative (Ali and Joe temporarily breaking their engagement) and positive (Ali and Joe getting re-engaged), and Louis is not going to stop any time soon, according to Urie.

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"Louis doesn't have boundaries with Joe. He doesn't really have boundaries at all! He clearly doesn't see the issue with this," he says. "Even though Louis loves Ali, suddenly the boundary's getting pushed up against him and he doesn't understand why. ... But he sees no reason to stop this meddling. He's an important part of Joe's life."

Does that mean it's up to Joe to learn to keep some things to himself and Ali? "The resolution is not something you might expect," Urie teases.

"We've established four people who love each other and get along. We are a tight foursome ... but at the core is still Louis and Joe's great friendship," Urie continues. "We get into a discussion in an upcoming episode about which one of us is more important, like who's the Simon of Simon and Garfunkel. ... Of course, I argue that I'm Simon and Joe argues that it shouldn't matter. It starts as business partners and it becomes a much bigger question. I'm sure that one of them realizes they're wrong and I'm sure one is me! But they're equally as important to each other — they're Simon and Simon. Poor Garfunkel!"

Partners airs Mondays at 8:30/7:30c on CBS.