What is this “Good vs. Evil”?

“The good man brings good things out of the good stored up in his heart, and the evil man brings evil things out of the evil stored up in his heart. For out of the overflow of his heart his mouth speaks.” - Luke 6:45

In the world today, there are so many contrasting perspectives and morals that people identify with that it’s difficult to decipher between what’s good and what’s evil. I mean, how did we even create this good vs. evil battle? Was it always there, from the beginning? One day, did we just evolve into creatures that had the ability to choose right from wrong? For Christians, there is something inside of them that helps them to realize what is good and evil, called the “Holy Spirit.” I am a Christian and I believe that good comes from Jesus Christ our Savior in Heaven and evil comes from the Devil in Hell. Not everyone believes the same way I do. I believe that homosexuality is immoral and that love was meant for a man and a woman. Obviously most of the world feels otherwise. Does that make my definition of good and evil in that scenario wrong?
What it boils down to is what one’s definitions of good and evil are for each situation. The world is so diverse and with diversity comes conflicting opinions and morals. This means that, by the world’s standards, there is no absolute good and evil. As a Christian, I believe that there is an absolute good and evil that is determined by God and explained in the Bible.