Is there any concrete, irrefutable evidence proving the existence of "God" (the one in the Bible).
Nope - it's all a 'personal' belief system. I quoted personal since many religions are an organized form of mind-control setup to benefit those in power at the 'head' of the religion or those leading the nation where the religion is being established.
When everyone thinks alike they are much easier to control and influence into doing the things you want them to do. And the participants feel more at ease when all those around them feel and think the same way - it helps take the edge and unease away.
Just look at how frequently organized religion trys to get it's followers to convert others.
"The one-celled animals reproduce by splitting, not sex. How could male and female be evolved into multicelled animals before they die from splitting? Did one Ameoba tell another, "Hey, why don't you become a female and I will be a male and we will have sex and produce baby ameobas."?
Also, how did evolution evolve pleasure during sex?"
Sex back in the day of one celled animals was not what you think it is, a male and a female interacting with some 'body' part that exchanges fluids. It's much more likely the first version of sex was the accidental exchange of RNA amongst an isolated community. That then gives that community genetic diversity and therefore gives them an advantage to survive environment change. If something then happens to wipe out all the other clones (based on their identical weakness to change) that reproduced by splitting, boom, sex has evolved as the dominant way to reproduce.
And why do you think there is pleasure during sex? Just to make it feel good say you can say "Thanks God, that was awesome!"? Get real - ALL life on this planet has one universal drive - to reproduce and propagate the species. What would be the best way to ensure things reproduce - why - you might find those individuals that found it felt good, did it more, had more off spring, and after a few generations out number the rest of the population, so boom - now pleasurable sex has evolved. Take some responsibility for your own life and see the world and your place in it for what it is - or perhaps that is just too scary.