“Whatever you are doing, work at it with enthusiasm, as to the Lord and not for people” Col 3:23 (NET)
It is normal that many give more efforts in working for God than working for man. Many believe God deserve the best and not man. The reason why many people are not faithful to their fellow men is because men often disappoint and neglect us. Many only know how to receive from you but do not give you anything in return. Unfortunately, we don't know that many of things we are doing are mostly to God.
“But a man named Ananias, with Sapphira his wife, sold a piece of property. However, he kept back part of the proceeds with his wife’s knowledge, and brought a portion of it and laid it at the apostles’ feet. Then Peter said, “Ananias, why has Satan filled your heart to lie to the Holy Spirit and keep back part of the proceeds from the field? Wasn’t it yours while you possessed it? And after it was sold, wasn’t it at your disposal? Why is it that you planned this thing in your heart? You have not lied to men but to God!” When he heard these words, Ananias dropped dead, and a great fear came on all who heard. The young men got up, wrapped [his body], carried him out, and buried him. There was an interval of about three hours; then his wife came in, not knowing what had happened. “Tell me,” Peter asked her, “did you sell the field for this price?” “Yes,” she said, “for that price.” Then Peter said to her, “Why did you agree to test the Spirit of the Lord? Look! The feet of those who have buried your husband are at the door, and they will carry you out!”  Instantly she dropped dead at his feet. When the young men came in, they found her dead, carried her out, and buried her beside her husband. Then great fear came on the whole church and on all who heard these things.”Acts 5:1-11 (HCSB)
Here was a couple who thought they are deceiving man (Peter) but learned their lesson in a hard way. God do directly punish us for the sin we commit against another person.

In Genesis 39, Joseph who was expected to lose his relationship with God due to his melancholic experience when he had a wonderful opportunity to enjoy himself but he said in verse 9
“… how then can I do this great wickedness, and sin against God?” 
He knew what actually he was asked to do was more or less against God and not against his master.
God created man in his image and made him His representative on earth, so whatever you do to your fellow human being - constructive or destructive, you are doing it to God.

“…To sum up, each one of you is to love his wife as himself, and the wife is to respect her husband” Ephesians 5:22-25, 33 (HCSB). 
Paul was writing the Ephesians couples to love one another with the illustration of Christ and the Church. You are to love your spouse not as they deserve but as God commands. When your spouse does not do what you expect, that should not reduce your responsibilities to one another. Anything you do to each other, God is the one to reward you. Do not pay evil with evil to your spouse because it is God that will judge you and He won't judge you by your reasons but by your actions. When he offends you, try to forgive him, not because it's not painful to you but because that's God command to you. don't say because he is flirting, you are not going to submit to him. Many would say if not for this or that condition, they won't marry each other; do not let this push you into taking negative actions because God won't evaluate your reasons for doing such before he will judge you.

“Servants, respectfully obey your earthly masters but always with an eye to obeying the real master, Christ." Eph 6:5 (MSG). 
Many do lie to their boss, which is very bad. Even if you are older than your boss, as long as he is your boss, respect him. When some employees are rebuked, they may decide not to go to work the next day. Some even fight their boss when he tries to discipline them. Some steals and extort their boss secretly. Don't look at the way he treats you, do your responsibilities as if it is unto God. Respect your physical and spiritual superior as if they are God. I remember a movie I watched sometime ago. There was this young vibrant anointed man of God was serving under the mentorship of his General Overseer. He is assigned sometimes to speak on behalf of the G.O. at programmes. Through his G.O. many knew him as he was always delegated by the G.O. to pray for some people and signs and wonders follows suit. After sometime, this young man of God felt the G.O. was too bossy on him; he decided to break away after listening to his friends' suggestions despite his wife going against it. One day, he had a dream where he saw himself washing plates with a white sponge; all of a sudden a white garment man appeared and snatched the sponge away from him. The man told him that he was no longer qualified to use the precious sponge again. As he tried to get it back from the man, another red and black garment man appeared and gave him a black sponge that he can as well use this also, so collected it and continued washing; then woke up from the dream frightened and confused. Since this revelation, anyone he prayed for, their problems multiplied, it got to a point that he had to pray for a pregnant woman who was travailing but needs a special miracle to give birth, as he laid his hands on the woman, she died in the process. This led to his arrest and remained in police custody. He was later bailed out by his former G.O. after his wife’s plea. Here was a man who thinks all his work in the ministry was to the glory and profit of his superior (G.O.) but was demoted by heaven for that stupid act.

Don't cheat anyone just because he is stingy. David sinned against Uriah but God was the one who punished him. David said
“Against you, and you alone, have I sinned; I have done what is evil in your sight…” Psalms 51:4 (NLT). 

Many go to church thinking they are favouring the pastor. A man found himself in hell just because he always had the thought that all tithes is only for the pastor's upkeep. He was therefore not faithful to God in the area of tithe.

When people don't do the way you expect, keep playing your own part because God is the one to reward you. Always think about the love of God upon your life and you won't get wearied of doing good.
Jesus said “Let evildoers do their worst and the dirty-minded go all out in pollution, but let the righteous maintain a straight course and the holy continue on in holiness." "Yes, I'm on my way! I'll be there soon! I'm bringing my payroll with me. I'll pay all people in full for their life's work”  Rev 22:11-12 (MSG)