Everything went to hell (not literally) after the whole garden of eden thing. Everything would have been fine I'd not for that, and everything bad can be traced back to that point. You also have to take into account that it seems like God's highest priority is our free will, so we can do whatever we want. God has never told anyone that we know of why he created humans, but from his actions, it seems logical to assume that he wanted people to share existence with and love him WILLINGLY. That is why we have free will. Also, it isn't a sin to be gay, it's a sin to do a sex with someone of your same gender. I'm catholic, so we also believe that if you sin and you truly regret it and confess it through the sacrament of confession, God forgives you and that sin is gone. God wants to love everyone, and he wants us to love him back willingly. It is our choice to sin, and thus turn away from God that gets us sent to hell.