How do people express love in modern society?
Your question uses the word 'love'.
In modern society this word is usually thought of as 'making love' or having 'sex'.
The reason is that in modern society people are basically selfish and are looking to fulfill their own lusts, and they tell a woman they love them, so they should have sex. Often they move on to another woman after they have got what they wanted from the first one.
There is a second different society that has a very different point of view.
They are a society of people who are true followers of Jesus, and see love and sex as two different things.
They have learned that love is caring very much for the best interests of the other person. So when they love someone they show it by caring, protecting, providing and serving that person.
When a woman finds these qualities in a man, she often wants to spend the rest of her life with him. They get married and he does not change, he continues to show the same qualities he did before he married her.
She is very appreciative, and returns the love in caring and nurturing him. In that condition they enjoy the imtimacy of married sex, in a deep and fuller way than the people who do not really care for each other.
This affection makes for a sense of security, and love is expressed through the life style, and sex is an expression of their love and caring. They tend to stay together for life, and help each other when times are tough.
God blessed man and woman and told them to reproduce and fill the earth.
That happens in the loving relationship where the children grow up and learn from the actions and attitudes of their parents. Those children become well balanced and tend to be more successful in life as a result.
For an understanding of the defintion of Love, (the old English word used was Charity) please read
1 Corinthians chapter 13.