In my experience partners who seem to be irritated by you and snappy irrationally are pushing down a deeper problem. Maybe he feels disloyal now he lives with you, maybe he is uncomfortable in your place and doesn't want to hurt your feelings. He is probably stressed that he has to deal with daughters marriage on his own without her mum's input.
You need a long, honest talk. If not I guarantee resentment will build and eat away at the relationship you have.
I know of 2 failed marriages to widowers. One, they met too soon [within 6 months of the bereavement], he wouldn't get rid of wife's clothes/photos/etc, the son wouldn't accept new wife, he wouldn't give up a hobby which took up big chunks of time, sometimes whole days. She persuaded him to move to another county, it didn't solve anything just tore him away from his support: brothers and sisters, nieces and nephews, friends.
The other couldn't cope with her new husband visiting his deceased wife's grave every weekend, and being upset.
It seems a difficult situation to negotiate, the loss of a wife which not the man's choice, so many raw feelings and trying to make another life with a new person must be confusing at times.