We can expect sin to end in the last days as stated in Isaiah 2:2, "And it shall come to pass in the last days, that the mountain of the Lord's house shall be established in the top of the mountains, and shall be exalted above the hills: and all nations shall flow unto it.."
From the beginning of creation in the book of Genesis God defines marriage as between one man and one woman. "God created man in his own image… male and female created he them. And God said unto them, Be fruitful, and multiply, and replenish the earth…" (Genesis 1:27 and 28).
As God created humanity, he began with a man and a woman. God created them to take care of His own creation, populate the earth, and have a relationship with Him. The man and woman were the perfect role models of a healthy and loving relationship. They felt genuine happiness.