A/N: SPOV
Severus was in his private lab, inhaling the steam over a cauldron as he checked the self-stirring cauldron simmering next to him. He was restocking Poppy's stores during the break, and was interrupted by a knock on his door.
"I am busy brewing, Albus." Severus called out, not even looking over his shoulder.
The door opened on its own, and Severus knew that it would have to be Nymphadora.
"Your Patronus was a doe." Tonks said, taking in the view of his private lab. She saw a chair by his chalkboard and sat down. It appeared that he had been outlining a new potion on the chalkboard, but was brewing in three separate cauldrons on the other side of the room.
"It was, Nymphadora. Then it staggered away and died at your feet. Albus was not amused." Severus replied, grinding up some seeds in a mortar and sprinkling them into the stirring cauldron.
"No, he wasn't amused at all. He thinks that I'm distracting you from your duties; that I'm going to be a liability to you and to the war." Tonks stood and walked over to him, careful to give him enough working space.
"As you can see, interacting with you isn't a distraction. I am quite capable of disciplining my mind to whatever tasks that I am faced with." Severus took the third potion off of the simmering heat and began to ladle it into bottles and cork them.
"Then look at me. Slughorn should be doing this anyways." Tonks put her hand upon his once he set down the final potion vial. "Don't prove him right."
"I'm not; I'm just busy right now." He dismissed her, pulling away and inspecting the self-stirring cauldron.
"Harry's Patronus was a stag. And Lily's was a doe. I know how to draw conclusions."
Severus took a breath, clearing his mind. "My last two decades of my life were defined by Lily. My love for her, my loss of her, and promising to keep her son safe and to defeat The Dark Lord. My Patronus has reborn itself into a new form."
"That doesn't mean that you cannot still fight You-Know... The Dark Lord. If anything, you've got a reason to live through all this, to survive and watch old snakeface die." Severus smirked at the name.
"I heard what you said to Dumbledore in the trophy room, and what he had said to you." She looked at him, surprised. He returned her a faint smile. "You don't survive as a spy without doing things like improving on the Weasley's extendable ears. You said my love for Lily had been twisted and that I was bent on a self-destructive mission to see The Dark Lord destroyed. I think realizing that was what finally killed my doe Patronus. Lily would like to see that I'm working for the Order, but not at the cost of me slipping further into darkness. She'd want to see me move on, and that's exactly what I did.
"Your Patronus changed and became a werewolf because of Lupin. Mine has turned into Y Ddraig Goch, the Welsh Red Dragon. Its motto, the motto of Cardiff, is: Y ddraig goch ddyry cychwyn. The Red Dragon Leads the way. Legend says that the Red Dragon was locked in a battle with an invading White Dragon, and that the red one wins. I usually don't put stock into legends, but I am curious as to who would be the white dragon if this were to be prophetic."
Severus turned off the other cauldrons and faced her. "Dumbledore has no right to say that there needs to be more happiness in this world and then pick and choose who can be happy. So sod his advice and his false platitudes. I plan on making and keeping you happy for as long as I can." He vanished the contents of the two remaining cauldrons and washed his hands. "Perhaps I can interest you in a fair snowball fight? Or perhaps a bit of dueling practice?" He offered his arm in an escorting manner.
Tonks smiled, taking his arm. "Severus Snape, not wasting away in his lab on Boxing Day. Let's see if you're a complete nutter and want to hit up muggle London for lunch."