Why is it a sin to love someone more than God?

It's called idolatry. Yes there are verses. Look it up.

God is love, to love them is to love God. God is in everything good in your life and do not separate you love for God with your love of family.

The FIRST COMMANDMENT says to love God with all your heart, mind and strength..
(Deuteronomy 6:5) and confirmed by Jesus Christ (Mark 12:28-30) You are probably
excused if you are not a person with any faith in God .. but anyone who is a genuine
Christian convert, born of the Spirit, gains understanding by the Spirit of Truth.. of the
Sovereignty and Lordship of our loving God who redeemed us from sin and death.

The scriptures make a clear parallel between the love and commitment of a man and
wife that should reflect the love and commitment of Jesus Christ (as "groom") to His
church (the "bride" awaiting His return) .. The relationship is that important to God.

That parallel doesn't tell you to love your wife less ~ but nor should anyone love God
less, IF they have genuine redemption that was initiated by the Spirit of God.

because God is jealous.

How did Jesus show that he loved his Father?

“I love the Father.” ... Nothing mattered more to Jesus than that.

John 14:31
31 But for the world to know that I love the Father, I am doing just as the Father has commanded me to do.+ Get up, let us go from here.

Mark 12:30
30 and you must love Jehovah your God with your whole heart and with your whole soul and with your whole mind and with your whole strength.’

If you loved them more than God then you would murder, cheat, steal, lie and do whatsoever you felt were necessary to do for them. If you love God more than them you will not murder, cheat, steal, lie and such for them.

John 14:15 If ye love me, keep my commandments.

Jesus warned his disciples not to love anything greater than their love for him or his Father in Matthew 10:37. Why? Because as our Creator and life giver, Jehovah (Psalm 83:18) deserve our complete love and devotion. Also, Jehovah appointed his son, Jesus as King of his kingdom and as such, we should imitate his example closely. (1 Peter 2:21)

What that means is that you always turn to God to know HOW to love them. God first, then others.

A person can better worship only God if they recite daily and with care the angelic psalter of the Blessed Virgin.

We all have emotional centers. For example, a person who is centered on his work is considered a workaholic. This attitude pushes everyone else away. Wives and children become a hindrance to duty.

We can also be centered on family which at first glance seems good. But it also creates a negative attitude towards other parts of life such as employment, friends, church, etc.

If we place our hearts on following Christ, all other centers are placed in proper perspective. We will love our family, be honest in our work, serve in the community, and treat others as self.

"He that loveth father or mother more than me is not worthy of me: and he that loveth son or daughter more than me is not worthy of me. And he that taketh not his cross, and followeth after me, is not worthy of me. He that findeth his life shall lose it: and he that loseth his life for my sake shall find it." Matthew 10:37-39

Apparently it's because the Christian God is pathologically insecure and jealous, and demands full and complete attention and commitment or else He feels bad about himself and lashes out like a small child.

Because no one loves you more than God

And the people who say they do may not even mean it

To some people God is supposed to come before anything, including other people. It's sad.

religious cults like to be top priority in the lives of cult members....