Why is being gay considered more sinful than being divorced or commiting adultery?

Sin is like cyanide, it is deadly in small or large doses.

Sin is also defined as missing the mark. If you hit the mark, you get the prize. If you miss the mark, you miss the prize.

If you head into h*m*sexual activity, you enter an addiction that causes you to miss out on something better. Genesis 1:27 states that God created man in His own image, male and female he created them. Therefore for every type of male DNA there must be somewhere a corresponding type of female DNA that is a compatible match for it. It is the enormity of the intended gift that determines the enormity of the sin that causes one to miss out.

Divorce and remarriage are allowed in some cases. Homosexuality is never approved. Adultery is also never approved.

All can be forgiven and restored through faith in Christ and the help of the Holy Spirit; deliverance can be instant but often it is long and difficult as in any case of addiction or allergic reaction. (addictions now are treated as allergies bringing on a strong and unusual response to stimuli that cause little or no response in others).

Hope this perspective helps.

First of all, if you are going to accept an answer from conservative biblical scholarship, you have to set aside the claim that Paul merely condemned "men acting/dressing like women." Romans 1:26-27 has been claimed to be addressing certain forms of sexual intercourse, not just dressing or acting like women. An additional point on this distinction is that h*m*sexual orientation, per se, is not condemned in many theologically conservative treatments of the issue, as opposed to h*m*sexual practice.

Here is one example of a theologically conservative group making a distinction between orientation and practice. The American Lutheran Church's 1980 Statement on Human Sexuality says:

We believe it appropriate to distinguish between h*m*sexual orientation and h*m*sexual behavior. Persons who do not practice their h*m*sexual erotic preference do not violate our understanding of Christian sexual behavior.

Secondly, you are precisely correct that scripture holds divorce in higher disregard than h*m*sexual practice. Those who hold it h*m*sexual practice to be a greater outrage are relying on extrabiblical, perhaps cultural or personal, motivations. Jesus himself has great outrage at divorce.

Matthew 19: Some Pharisees came to him to test him. They asked, “Is it lawful for a man to divorce his wife for any and every reason?” “Haven’t you read,” he replied, “that at the beginning the Creator ‘made them male and female,’ and said, ‘For this reason a man will leave his father and mother and be united to his wife, and the two will become one flesh’? So they are no longer two, but one flesh. Therefore what God has joined together, let no one separate.” “Why then,” they asked, “did Moses command that a man give his wife a certificate of divorce and send her away?” Jesus replied, “Moses permitted you to divorce your wives because your hearts were hard. But it was not this way from the beginning. I tell you that anyone who divorces his wife, except for sexual immorality, and marries another woman commits adultery.”

It is worth noting that while divorce was not part of God's original intent / design, for those who were determined to divorce, God made a provision (through Moses) for them to do that in a respectful way.

This is in stark contrast with h*m*sexuality, which, throughout the entire Christian canon is characteristic of deep depravity (cf. Sodom, Rom. 1), and leads to the severest condemnation and judgment from God -- every time it is mentioned.

Sin is sin, but one is tolerated (cf. polygamy), and one is severely, consistently condemned (cf. idolatry.)

Regarding the alleged distinction between orientation and practice, we should probably consider Jesus' Sermon on the Mount, where He explicitly refutes such thinking and defines even perverse thoughts as sin.

So what is a "h*m*sexually-oriented" person to do?

those who belong to Christ Jesus have crucified the flesh with its passions and desires. -Galatians 5:24

we are taking every thought captive to the obedience of Christ -2 Corinthians 10:5

Set your mind on the things above, not on the things that are on earth. -Colossians 3:2

Finally, brethren, whatever is true, whatever is honorable, whatever is right, whatever is pure, whatever is lovely, whatever is of good repute, if there is any excellence and if anything worthy of praise, dwell on these things. -Philippians 4:8

...which, incidentally, is good advice in general for any such struggle with the flesh.