When a spouse dies there is noting immoral about getting remairred.
But when you divorce one spouse and marry another you are (most likely) guilty of adultery according to scripture.
Scripture talks about divorce and it is not considered a good thing. But scripture has even stronger words against get remarried.
Depends on the situation. Your myopic view of mathew 19 probably hurts alot of people. We all know its not ideal but to call it adultry for all cases is disingenuous at best. It is imparitive that we look at the audiance that Jesus was talking to and their beliefs on divorce and remarriage. I agree it is unfortunate that the bible does not list out verbatim all the possible scenarios where divorce and remarraige is valid but we can use common sense. I do not feel as if I commited adultry when my ex wife decided to no longer full fill her marital duties so I divorced her and remarried, had she not continually sinned against me I would not have divorced.