I have heard you say that homosexuality is not genetic and that the behavior can be changed. Does this mean I must become a heterosexual and prove it by getting married to a woman before God will let me into heaven?
No. Marriage is not required of anyone. It is only required if you wish to have sex (Hebrews 13:4). God's law states you are not allowed to have sex with another man (I Corinthians 6:9-10), to lust for it (Mark 7:21-23), or to promote it as being acceptable (Romans 1:32), which is exactly the same requirement on those wanting to commit fornication or adultery.
Then I can can still be homosexual. I just can't have sexual relations and live without the possibility of a relationship. If I prayed every day for a thousand years, I still wouldn't feel sexual attraction for women. Most straight men I know have their libido go into overdrive at the sight of a woman they think is beautiful. I look at women and think, "She's very pretty" or "She's gorgeous!" No jealousy at all like some gay guys, but still no sexual arousal.
The Bible's definition of homosexuality is someone having sex with a person of the same gender. "You shall not lie with a male as with a woman. It is an abomination" (Leviticus 18:22). What you happen to find sexually arousing has little to do with whether you decide to have sex with another male or not.
This view is consistent with other forms of sex. Just because a guy is aroused by the look of a female, it doesn't make him a fornicator or an adulterer. Yet, his arousal may encourage him into an area of thought or action that is sinful.
Sexual arousal is not defined as sinful. For guys especially at the onset of puberty it is uncontrolled. It is referred to as spontaneous erections because anything, everything, and nothing at all causes the body to respond. It is also trainable as seen over time, fewer things trigger arousal.
"But each one is tempted when he is drawn away by his own desires and enticed. Then, when desire has conceived, it gives birth to sin; and sin, when it is full-grown, brings forth death" (James 1:14-15).
Uncontrolled desires can lead to lust. Lust can lead to sinful action. Sin when fully given into leads to death.
Lust is distinct from desire or temptation. Temptation is the offering of getting what you desire but with the catch that you have to break a law of God to get it. Lust is when a person finds the offer acceptable and begins to justify in his mind that the broken law is fine in this particular situation. Temptation is not wrong, but lust is wrong. "For from within, out of the heart of men, proceed evil thoughts, adulteries, fornications, murders, thefts, covetousness, wickedness, deceit, lewdness, an evil eye, blasphemy, pride, foolishness. All these evil things come from within and defile a man" (Mark 7:21-23).
Actions can be changed. After listing out sins, such as adultery, fornication, and homosexuality, Paul noted, "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 6:11). For some, the change in action also brings about a change in desire.
I mention all of this to state that no one is a sinner just because they exist. There are laws given by God for the benefit of mankind (Deuteronomy 10:12-13). Breaking those laws is sin. Wanting to break those laws to the point of justifying it in your mind is lust. But if you are doing neither, then you are not in sin and should not be classifying yourself in a category of sinfulness.