Does God hate all adulterers and fornicators? Are they all destined to burn for all eternity in the fires of Hell?

Your question is misleading in that it doesn't consider the possibility of sinners leaving their sins behind. We are warned, "Marriage is honorable among all, and the bed undefiled; but fornicators and adulterers God will judge" (Hebrews 13:4). But Peter also states, "The Lord is not slack concerning His promise, as some count slackness, but is longsuffering toward us, not willing that any should perish but that all should come to repentance" (II Peter 3:9). Therefore, if people commit sexual sins and do not turn from their sins, then justice requires that they be punished for their sins.

But sexual sins do not have to be permanent. We see this in Corinth. "Do you not know that the unrighteous will not inherit the kingdom of God? Do not be deceived. Neither fornicators, nor idolaters, nor adulterers, nor homosexuals, nor sodomites, nor thieves, nor covetous, nor drunkards, nor revilers, nor extortioners will inherit the kingdom of God. And such were some of you. But you were washed, but you were sanctified, but you were justified in the name of the Lord Jesus and by the Spirit of our God" (I Corinthians 6:9-11).

The Lord is righteous and stand opposed to wickedness of any sort. When people reject God and prefer to wallow in their sins, then yes, God hates the wicked in contrast to His love for the righteous. "The LORD tests the righteous, but the wicked and the one who loves violence His soul hates. Upon the wicked He will rain coals; fire and brimstone and a burning wind shall be the portion of their cup. For the LORD is righteous, He loves righteousness; His countenance beholds the upright" (Psalm 11:5-7).

But he hates those who don't repent of these two sins?

Isn't that what I pointed out? God hates those who want to remain in sin -- any sin -- including adultery and fornication. That is why God has worked so hard to save people from their sins. God wants to love His creation and so He seeks to release them from the bondage of their sins. "For when we were still without strength, in due time Christ died for the ungodly. For scarcely for a righteous man will one die; yet perhaps for a good man someone would even dare to die. But God demonstrates His own love toward us, in that while we were still sinners, Christ died for us" (Romans 8:6-8).

See also:

Questions and Answers regarding Sin
Questions and Answers regarding Fornication
Questions and Answers regarding Adultery