Disclaimer: I do not own Hawaii Five-0 or any of the characters from Hawaii Five-0. If I did own them, Steve and Danny would be shacked up in Steve's beachside home with custody of Grace and knocking boots every night.
This constant back and forth had to stop. It annoyed Catherine to see her Steve banter and flirt with his work partner constantly when they were in each other's presence. It was bad enough that she had to tolerate it when she was ship bound, but now that she isn't it was a thousand times worse. She was sick of it. If Steve wanted to constantly banter and flirt with someone then it should be her and not some annoying, loudmouthed, little man from New Jersey.
That night Catherine makes a nice meal for her and Steve, in Steve's kitchen. She is going to make clear to Steve that he needs to stop his unacceptable behavior and work with her on their relationship. That work includes letting her move into here, his house, and out of her little rental house. After placing the last dish on the table, she steps back to admire her handiwork and hears the front door open.
Turning with a smile, she starts to welcome Steve home only to stop as she sees Steve's partner with him. With her anger fast rising, she snaps, "What the hell is Danny doing here? I told you that I was fixing dinner for us. I told you that I need to talk to you. That implies that I want to talk to you alone! Instead we have a third wheel and I'm sick of it. I'm sick of listening to you banter with him. I'm sick of watching you flirt with him. I'm sick of you touching him. I'm just flat sick of him, Detective Danny Williams, all together! I want him gone, Steve. I want him out of your life. I planned on talking to you about this over dinner. I don't care about your friendship or partnership. I am your girlfriend, not him, and I want him gone now."
Steve and Danny are stunned by the vile and virulent verbal attack from Catherine. Recovering first, Steve steps in front of Danny and glares at her. What she wanted is never going to happen, he cares too much for Danny to just abandon him. That she would ask him to, well it is just the final thing he needed to prove that she isn't the one for him.
In his Super-Extreme-SEAL-of-Death tone, as Danny calls it for it's quiet deadly qualities, he says, "Get your things and get out, Catherine. Our relationship started out as a friends with benefits, you scratch my back and I'll scratch yours thing. I thought we might be making it more, but now...now it's done. We are through. You want me to just drop Danny because what? You don't like how we interact with each other? Why? Because you're jealous? I don't care. I have never cheated on you Catherine, but I will never end my relationship with Danny for anyone. We are friends and partners. Since it bothers you so much, get out and stay away! You obviously don't know me."
Now Catherine is stunned. She had been certain that Steve would choose her. They have history and the Navy. She looks from Steve to Danny, only to see Danny looking shellshocked by this whole event. Not willing to accept that she ruined her relationship with Steve and leave, she snarls at Danny, "I hope you're happy. It's your fault Steve just broke up with me. We could have been happy. We could have had a family. Instead we have you to thank for break Steve and I up. We have you to thank for ruining Steve's naval career. You've ruined everything and I hope you're happy about it!"
Now normally Danny is a fairly self assured man, but witnessing this horrifying fight between his best friend and his best friend's girl has thrown him off his game. Instead of being able to shrug off her attack as just heat of the moment words, he flinches back behind Steve for safety and fear. Had he ruined Steve's career? Had he ruined Steve's chance at happiness? Had he ruined Steve's chance for a family?
Hearing Catherine's bullying lies and seeing Danny flinch out of his peripheral vision snapped the last of Steve's control on his anger. Advancing on Catherine, he growls, "Get the hell out! Danny has done absolutely nothing wrong. He hasn't ruined anything. You have, Lieutenant Rollins! You are out of line with your attack and your lies. Now get the hell out of my house before I have you detained for trespassing!"
Catherine steps back from Steve's advance on her in fear. She finally realizes that she's pushed Steve too far and a strategic retreat is required at the moment. Confident that if she leaves now, she can get Steve to forgive her for tonight like he did over her lies about his mother. Gathering her purse and keys, she pushes past the men to the door. Opening it, she pauses to look back over her shoulder at them and says, "This isn't over yet. I'll be back for the rest of my stuff in a couple of days, Steve, and I want to talk to you then."
"There is nothing else to talk about Lieutenant Rollins. I'm finished with this. You want to keep on thinking you can get your own way, fine by me. But I will not be getting back together with you. We might be able to repair our friendship, but we'll never be more than friends again," replies Steve before he turns away from her and towards Danny, "Goodbye Lieutenant."
Wrapping his arms around Danny as the door slams, Steve takes stock of all that has been said. While he is sad that his friendship with Catherine is ruined and truly hopes that someday they might repair it, he is also relieved for their romantic relationship has ended. Not wanting to continue thinking of his former lover, Steve focuses on the best thing in his life and his arms. At least at the moment.