If you have a weak constitution for sexual perversion do not read

[Chopper]

Would this also apply to Christians who go to other religions More like leave the truth/God/ the way of righteousness etc.. than "go to other religions," but I digress) and come back? Or does that mean that they were never saved?

1 John 2:19
19 They went out from us, but they were not of us; for if they had been of us, they would no doubt have continued with us: but they went out, that they might be made manifest that they were not all of us.

It very well could mean that they were never saved to begin with. If one leaves traditional Christianity and joins with an Eastern religion like Mohammedanism or the like, They have become lost and can't come back.