Penelope shouldn't feel this sad but she does. She gets it really she does, Derek has a family now he can't afford to be in the line of fire anymore. She gets it but it doesn't stop her from drowning her sorrows in alcohol. Grabbing a bottle of wine, she is about to pour a glass when she hears a knock on her door.
Opening it she is shocked to find the former agent at her door, with alcohol. "Are you just going to stand their or let me in baby girl?"
Something tells her this is a bad idea but her best friend is standing at her door and who knows when they'd be able to hang out again. He has a baby now and she has work. It doesn't hurt that he brought alcohol, she is so down with getting drunk.
So against her better judgement she lets him in. They talk and dance and get really really drunk. Its passed midnight and their both wasted when she feels his lips on hers.
The logical part of him knows he has a wide and newborn son. He loves Savannah just not how he loves Penelope. It doesn't help that he's drunk.
She's shocked and knows whats happening is wrong but shes too drunk to stop him. When the kisses become less innocent she knows she should draw the line. She likes Savannah she really does. Penelope just happens to like the feeling of Derek's lips on her more. For the first time she allows herself to be selfish.
He doesn't write her a note when he leaves and she doesn't care. He moves on with his life, she goes back to work. Shes extra sad and everyone just assumes its because him leaving hits her the hardest- they were close after all.
Derek goes back home to his wife and son but the feeling of Penelope in his arms never leaves his mind.
When Penelope takes the test shes at home and shes drunken about five gallons of water to pee on ten different test. They all come back positive and she cries for a good hour. She debates about calling someone from the team but their still grieving over losing him. She debates about calling him but doesn't want to be a home wrecker. In the end she decides its not their baby but her baby and they'd be fine. She doesn't call him and has no intention of telling him ever. Penelope goes to bed with tear stained eyes. A part of her knows what shes doing wrong but she can't, won't make him chose between his wife and herself. She's not that selfish.
Hotch calls them in for a case five hours later and for the first time in forever shes late. She's not dressed exotically and shes sporting no make-up. He decides shes not alright but assumes she just need time to get over Derek leaving. He doesn't know how far off base he is.