There is only one GOD and always will remain ONE ,but He is called by other names
such as : Elohim, Melchizedek, Christ, Jehovah etc.
E.g. you are one person but am sure you have more than one name but at the end of the day there can only be one you.
The catholic teaches that there are three God's if there was i'd be so confused to know whom to pray to.
God say to Moses on the mount I AM THE I AM. He never say we are..... Three God's is a myth of satan and it's what lead people to idolatry etc.