The turn of current events had Achilles in a state of unrest. He was already emotionally broken, but now the wound he'd covered up with his time spent with Penthesilea had reopened. Those cuts were so deep they hadn't even closed over to leave a battle wound. He had so freely given up part of himself for a life with Polyxena and being deserted and felt as much a betrayal as when she gave Paris his secret those centuries ago during the war. He was as defeated then as he felt now. He'd softens a little with Patroclus' pledge to be by his side---his once time companion and comrade in arms.
The war Achilles fought now was in his head. He was conflicted and distraught. Not only was Polyxena back, but the son he failed to ever be a father to. It was salt on that festering wound. With Polyxena he'd had such a foreseeable future with a child, and once she lost that baby their future crumbled. So had he. He would not lie to himself that after Patroclus left him he wept. He wept for the what might have been and the now. He was on a fast downward spiral, and only Penthesilea seemed to be able to see that cry for help.
He came to her that way, broken and not as enthused with his life as it was. He had no idea to take charge of it, just headfirst and with his armor on. The moment he came into her apartment, locking the door behind him, he met her in the kitchen. He was as worn looking as he felt, but he greeted her with a kiss on the cheek as he did when they were trying to figure out their status. He'd been brutally honest with her then, his heart was cold, but there was a tiny bit of warmth that she had started to provide.