A lot of us have trouble with this emotionally as well. However, Jesus taught the reality of hell, He is my Lord, I believe Him. The punishment for sin seems extreme because we do not understand the holiness of God. he punishment of Jesus to redeem us from the penalty of sin was also extreme.
Hell is eternal separation from God. Oddly, it is a result of God's love. A loving God will not force us to choose Him. If we reject Him and His gift of grace He will not force us into eternal relationship with Him. We are eternal beings so we will live forever either in relationship with God or apart from God. So the choice is ours. Heaven - a place of extreme reward or Hell - a place of extreme punishment.