for the believer, suciide seems like a pretty selfish thing to do (one reason being that you're not doing the will of god (the will of god is kinda like what he has planned for you and what he wants you to do in your life) another reason is that you might have others that love you and need you... if you are a believer, you won't go to hell no matter what it says in John 10:29 My Father, which gave them me, is greater than all; and no man is able to pluck them out of my Father's hand.
this verse refers to those who have believed to god
the case with judas iscariot, he must've not been saved in the first place, much like there's many many people in the church today, who claim to be christians but never really fully understood the plan of salvation, they have not put their trust fully on jesus christ, you can act like you're a christian, you can talk like you're a christian, but you better make sure you have a connection with jesus christ, not some religion, which is really important
It says in Matthew 7:22-23 (King James Version)
Many will say to me in that day, Lord, Lord, have we not prophesied in thy name? and in thy name have cast out devils? and in thy name done many wonderful works?
And then will I profess unto them, I never knew you: depart from me, ye that work iniquity.
This speaks of those pretenders who believe that it's acts or works or crawling on their knees for hours or following jesus for 3 years on the earth (like judas did), unfortunately there are those who are so close to the knowledge of God but do not have the faith to accept him by faith alone
the case with saul is different, back in the old testament days, christ has not died on the cross yet, in the old testament days, the way to be saved was to have faith in the christ to come, soul as the first king of Israel would have to have known this especially, one of the requirements as a king of Israel was to read the history of Israel and the Pentateuch, which was the first 5 books of the bible and only books written at that time penned by Moses, not only did they have to read it, the king would have to re-write the whole pentateuch in his own handwriting, this ensures taht he does not miss any part of the commandments God placed on the Israelites, so in essence, each king of Israel had the opportunity to be saved, and lead the people of Israel in the ways of God, Saul having known this and believing in Christ was coming must have been saved ( i say must have because i do not know the true heart of man as i am not God who is the only one who can know)
summary - suicide has nothing to do with going to heaven or hell
i hope this answers ur question