This is, in my humble opinion, what should have happened at the end of Damaged, when Kevin spoke to Rossi about Penelope and him.
Possible Spoiler for Damaged. Season 3
Penelope was busy running routine maintenance on her babies when Derek suddenly opened the door to her office and rushed in. Penelope jumped and swung her chair around. When she realized it was Derek a smile appeared on her face, the kind of smile she gave only to him. "Hey there hot stuff you startled me" she said.
"What's this about you and Kevin and why haven't you said anything to me?" he asked her.
He took Penelope by surprise. The smile quickly disappeared and the expression that replaced it was total confusion. She wasn't really sure what he was talking about. Derek had known that she and Kevin had been seeing each other; in fact he was the first to find out. "What are you talking about Derek, you knew that we had gone out several times" she said. "Why are you so upset?"
Derek couldn't believe it. This was the one person he talked to about EVERYTHING. They told each other their deepest darkest secrets. At least he thought they did. There was nothing he wouldn't do for her. She kept this from him and even when he confronted her about it, she lied to him. Yea he knew they had gone out on some dates, so what? Kevin's chat with Rossi wasn't JUST about some dates. Obviously there was more to this. Hell even JJ. seemed to know more about it than him.
"I'm done! I can't keep doing this." He said and with that he turned around and walked out, slamming the door to her office. "Derek!! Derek come back!!" she yelled out, but he was gone and she was totally confused.
Derek walked into the bullpen, picked up his ready bag and told everyone he was going home. "Hey, what about our drinks?" Emily said. "I'll take a rain check Em; I'm not in the mood." He replied. He looked up towards Rossi's office and noticed that Kevin was still there. He tightened his jaw and stared at Kevin for a few before turning around and walking away.
"What's up with Derek?" Emily said. JJ smiled. "What do you think is wrong with him?" JJ looked at Emily and nodded towards Rossi's office. "Ohhh you think that's it?" Emily asked. "You saw how he got when he found out that Kevin wanted to talk to Rossi. Didn't you see how he stormed out of the Bull Pen?" JJ said.
"Wow, I can't help but feel for the guy, but you keep someone at arm's length long enough and they are bound to find another set of arms to settle in." Emily said.
JJ.'s phone rang, she looked at the caller ID and saw it was Penelope and answered. "Hey Pen, what's up?"
"JJ is Derek there?" Penelope asked. "He just left about 3 minutes ago, he's probably still in the parking lot" JJ told her. "Try him on his cell"
"I have, he won't pick up. Do you know what's wrong with him?" Penelope asked.
"Give him some time Pen, he needs to be able to lick his wounds" JJ said.
"Huh? What wounds?? What are you talking about? JJ stay there I'm on my way out" Penelope said.
"I'm about to Hello?? Penelope??" JJ looked at her phone and saw the call had been disconnected. She looked at Emily and sighed. "I don't think she knows about Kevin talking to Rossi. If she doesn't this going to go south real quick!" JJ said. Both girls turned towards the entrance of the bull pen when they heard Penelope's heal clicking on the floor. Penelope had walked into the pen at such a fast pace that her focus was only on JJ. She hadn't even noticed that Emily was there, even though she was standing right next to JJ.
"Is he hurt?? What happened?? What wound are you talking about?? JJ ANSWER ME!!" Penelope said in a tone that almost desperate. "I would but you need to give a few seconds between questions in order to do that!" JJ said.
"I'm sorry, he just took me by surprise and I'm a little confused about what's going on." Penelope said.
"How are things with you and Kevin going?" JJ asked.
"Kevin? I don't want to talk about Kevin JJ; he has nothing to do with this. I want to know what's going on with Derek!" Penelope said, almost yelling.
JJ looked at Penelope and realized she had no idea what was going on. She nodded her head towards Rossi's office hoping that Penelope would catch on and look herself. Penelope looked over to see what JJ was trying to show her and wound up doing a double take. At first the scene hadn't registered in her brain, but when she realized who was there she froze.
"Whaaat? WHY IS HE IN THERE??" She yelled. "What is he talking to MY Boss about?" I'm going to KILL HIM" she growled. Then suddenly it all came together. She went over Derek's words in her head. "Kevin's chat with Rossi wasn't JUST about some dates. Obviously there was more to this. Hell even JJ seemed to know more about it than him" Derek had said. Penelope now understood what Derek was talking about. It was more than anger, it was pain. He thought she was hiding this from him. She needed to talk to Derek. She had NO clue that Kevin was going to do this. How could she know? She had made it clear to him that he wasn't to discuss this with her superiors. She had even threatened him! She knew he was committed to their relationship, but she also knew she wasn't sure they even had one. Not like HE thought they did anyway. You can't give your heart to someone completely when it already belongs to someone else.
Penelope looked over at JJ and Emily and said "I gotta go!" and with that she quickly walked out of the bull pen and headed towards Esther.
JJ and Emily watched her leave and turned to each other. As if it had been planned they both said "It's about time!" Laughing at the coincidence of their words JJ added "What I wouldn't give to be a fly on THAT wall." Emily simply nodded in agreement.