Second to having a miserable baby, having a miserable partner is challenging. Fortunately, they are articulate beings and have more than varying intensities of wails to communicate with. When my husband was grumpy I administered a few well-intentioned platitudes but they didn't really seem to help.
During a calm moment, I asked him what I could say when he was upset and he suggested reminding him that he DOES love the baby. Simple! I tried it when his mood began to disintegrate and it worked! I felt reassured that I could help him revibrantise in an empathetic yet accurate manner. so I thought I'd mention it in case it helps you!