inconstant
/ɪnˈkɒnstənt/Definitions
1. adjective
unreliable or changeable in one’s affections, loyalties, or actions
“The inconstant weather made it difficult to plan our outdoor wedding.”
2. noun
a person who is unreliable or changeable in their affections or loyalties
“He’s known as an inconstant friend, always making and breaking promises.”