Relationship problems

I have a two month old daughter and ever since she was born the relationship between me and my partner has been awful. And on top of that, he’s keeping secrets and lying about things and his excuse is the stress is getting to him.... we are both stressed, we are both tired. But you don’t See me hiding and lying about things? I don’t even know what to do anymore. I hate that my baby girl is around all this chaos and I hate that we end up arguing in front of her. She’s innocent.