Will those who have sex before marriage & don't have a chance to repent before dying go to hell?

Yes they will as all others who don't repent.

Yep, most likely.  They shall be purified of their sin, taught the gospel of Christ (1 Peter 3:18-20; 4:6), be redeemed in "times of refreshing" as they individually pay "the utmost farthing" for their sins, and be prepared for the resurrections and final judgment.  Hell is never forever.  There is only finite punishment for finite sin.  God's love, justice, and mercy are all intact.

But it's a better idea to repent (or abstain) now and avoid hell altogether.  We get better rewards that way.  (St. Paul mentioned three glorious resurrections, each of which offers its appropriate reward[s] in eternity, e.g., the three heavens that are available to those who arise in the Celestial ("heavenly") resurrection.  Jesus truly can reward us according to our works.)

ONLY GOD CAN JUDGE, BUT GOD DOES STATE THAT IF A PERSON DIES IN MORTAL SIN AND DOES NOT SEEK FORGIVENESS BEFORE DEATH, WHICH COULD COME ON SUDDENLY AND WITHOUT WARNING, THEY WILL BE CONDEMNED BY THEIR OWN CHOICE.

SATAN ONLY HAD ONE CHANCE TO REJECT GOD OR NOT AND HE CHOSE TO REJECT GOD. GOD GIVES US MANY MORE CHANCES AND THE SACRED HEART OF JESUS AWAITS WITH OPEN, LOVING, FORGIVING ARMS FOR ALL THOSE WHO WILL SEEK HIM WITH A HUMBLE AND SINCERE HEART.

ALSO, >>>

GOD DOES NOT CREATE YOU HOMOSEXUAL, BISEXUAL, LESBIAN, IF THAT WERE THE CASE THEN HE MAKES ADULTERERS, FORNICATORS, MURDERERS, BANK ROBBERS THAT WAY TOO. THEN THERE WOULD BE NO SINS. SEE HOW IT DOES NOT MAKE SENSE TO BLAME GOD FOR WHAT YOU CHOOSE TO DO BUT,

LET ME TELL YOU THAT THEY ARE PRECIOUS TO THE LORD OUR GOD AS ALL OF US ARE. NOW IF YOU HAVE IMPURE THOUGHTS OR TEMPTATIONS IT IS NOT A SIN. It's ACTING ON THEM THAT IS THE SIN. IT DOES NOT MATTER IF ITS OF A MAN OR A Woman. ALL LUST IS IMPURE AND GOD HATES THE SIN BUT TRULY LOVES YOU. IF YOU ARE TRYING TO BE GOOD, YOU ARE DELIGHTING GOD VERY MUCH BECAUSE IT IS DIFFICULT SOMETIMES TO RESIST BUT IF YOU ARE TRYING JESUS(GOD) WILL HELP YOU BACK AND STRENGTHEN YOU BEHIND BELIEF. THIS IS DONE BY RECEIVING HIS BODY AND BLOOD, SOUL AND DIVINITY AT HOLY COMMUNION, AND PRAYING IN SECRET TO HIM, HE SEES YOU IN SECRET AND WILL REWARD YOU AT THE PROPER TIME.

YOU ARE SPECIAL BECAUSE YOU ARE RESISTING DOING EVIL JUST FOR GOD. IF YOU DID NOT HAVE THE TEMPTATIONS THERE WOULD BE NO GREAT STRUGGLE. LET ME TELL YOU HOMOSEXUALS DO NOT GO TO HELL FOR HOMOSEXUAL THOUGHTS JUST LIKE ADULTERERS DON'T. IT IS THE FALLING INTO THE LUSTFUL SINS AND NOT ASKING FOR FORGIVENESS BEFORE YOU DIE THAT PUT A PERSON INTO HELL NOT THE TEMPTATIONS. REMEMBER JESUS WHEN CARRYING HIS CROSS FELL THREE TIMES BUT GOT RIGHT BACK UP IN TERRIFIC PAIN AND MOVED FORWARD JUST FOR LOVE OF US AND HE IS LEAVING US AN EXAMPLE THAT WHEN WE FALL GET RIGHT BACK UP JUST FOR LOVE OF HIM AND ASK FOR FORGIVENESS WITH A SINCERE HEART AND YOU WILL BE FORGIVEN EACH AND EVERY TIME. DON'T YOU THINK OR LET ANYONE TELL YOU THAT YOU ARE A HYPOCRITE BECAUSE YOU ARE NOT, ESPECIALLY IF YOU ARE SINCERE AT REPENTANCE, THE LORD KNOWS AND YOU KNOW IF YOU ARE TRYING OR NOT. IF YOU ARE TRYING THAT'S ALL GOD ASKS OF YOU, HE WILL WATCH OVER YOU IN A VERY SPECIAL WAY AND IN TIME (It's NOT DONE OVERnight) YOU WILL BE CURED OF ALL YOUR SEXUAL DESIRES IN HIS NAME. DID YOU KNOW THAT ST AUGUSTINE WAS A SEX ADDICT AND HE TURNED TO GOD FOR STRENGTH AND IS NOW A SAINT. YOU SEE HOW TEMPTATIONS GOT HIM TO BE A SAINT, GOD WATCHED HIM CLOSELY AND KEPT HIM SAFE, BECAUSE GOD KNEW HE WAS TRYING, JUST LIKE HE IS WATCHING OVER YOU. 

GOD WILL ACCEPT THIS IF YOU CANNOT GET TO CONFESSION

A PERFECT ACT OF CONTRITION!

Oh my God! I am heartily sorry

for having offended Thee and

I detest all my sins because

I dread the loss of Heaven and the pains of Hell;

But most of all because I have offended Thee, My God,

Who art all-good and deserving of all my love.

I firmly resolve, with the help of Thy grace,

To confess my sins, to do penance,

And to amend my life. Amen.

God alone knows the answer to that question. Fornication is a serious sin, clearly forbidden by God. However, God alone is the Judge. We are not.

Yes for the wages of sin is death. but the gift of God is eternal life in Christ Jesus our Lord Romans 6:23. it only takes one unforgiven sin to cause us to go to hell. if we sin on purpose after we have been baptized into Christ we are crucifying out Lord all over again and counting the covenant as no good. we can not sin on purpose we if we are saved are saved by the grace of God unmerited unearned undeserved favor of God. Romans 3:10,23  for there are none that are righteous no not one. For all have sinned and fallen short of the glory of God. Hebrews 13:4 Marriage is honorable among all, and the bed undefiled; but fornicators and adulterers God will Judge. Thanks for the question.

When it comes to judgment and who will "go to hell", I don't like to be the judge. God is their judge, and even he says that some he made for the day of destruction. What I do know is that there is only one way into heaven. That is through putting your faith and trust in Jesus. Those who do not, will face the coming judgment by being weighed by their deeds and will be found lacking. Each of us know good and evil, even those who have not heard of Jesus. We know what is wrong and right and we make choices that have consequences. I can't say where that person will end up or what will happen upon their deathbed or last moments. I don't know their heart or struggles. I don't know if they have fallen into the sin or fully endorse it. All of these are important it seems when it comes to the judgment of God and I usually just say that you should steer clear of sin and treat "today" as the day you come before God, as who knows when you will perish?

If that's true, I'm in some deep sh𝐢t.

As no Hell exists, other than as a small town in Michigan, nope.

No.  A person goes to hell if they refuse to believe in the Lord Jesus Christ.  They are forgiven all sins past and future by believing in the Lord Jesus Christ.  So dying during sexual sin leads to heaven if they believe in the Lord Jesus Christ.  Dying for any reason as an unbeliever, leads to hell.  Jesus came to save sinners.  The Lord Jesus Christ is God, and He loves you.  Believing in the Lord Jesus Christ means being forgiven all sins past and future, and means going to heaven and not hell.  Death leads to immediate heaven or hell, and it is too late to be saved, after death.  All believers still sin.  See 1 John 1:8.  To be in heaven and not hell, believe in the Lord Jesus Christ, who is God and who died on the cross and shed His blood to pay for all of our sins in full, and who was buried, and who resurrected from the dead.  The only way to avoid hell is by believing in the Lord Jesus Christ, without adding any of your own works.  See Romans 4:5, 1 Corinthians 15:3-4, and John 3:16.

Hebrews 13:4 tells it.