Many grieving folks feel pain when they have a moment of happiness after their loved one has died. They often describe feeling disloyal to the one who has died if they have an emotion that is not sadness. Or they describe feeling guilty for having pleasure when their loved one cannot be there to enjoy the experience.
A happy moment after a loss may sneak up on you. You may feel confusion when some light enters the darkness. Sadness is a connection to the one who has died, and happiness may seem like a break in that connection, but these moments provide something you need in this dark time.
Treat these occasions without self-judgment. You are not disloyal, and you are not doing anything wrong. Your love and loyalty to the one you miss is not diminished when an instance of happiness occurs.