Perhaps, the passage most fundamentalist Christians (who actually know something about Biblical interpretation) quote most often to condemn gay folks is the one referenced in the title. However, I (along with many other progressive Christians) still believe that they are interpreting this passage incorrectly. Some passages require a bit deeper understanding of the relevant history, the linguistic issues, and even a bit of science (and, where various cultures were at on the science of the related issue). Such is likely the case for interpreting Romans 1.
Here is the King James Version (I am always tempted to change King to Queen when I write that -- sorry) of Romans 1:26-27:
26) For this cause God gave them up unto vile affections: for even their women did change the natural use into that which is against nature:Let's discuss the relevant issues below the orange cheeto.
27) And likewise also the men, leaving the natural use of the woman, burned in their lust one for another; men with men working that which is unseemly, and receiving in themselves that recompense of their error which was meet.
Romans is a letter that Paul (Saul of Tarsus) wrote to the Christian church in Rome. The language used is Koine Greek. It was written during the rein of Nero, one of the most infamous emperors in ancient Roman history (although a number of them compete for that title).
Let's just give a very brief summary of the first three chapters of Romans because it helps us in understanding this passage. Chapter one is about the gentiles (goyim) and how they had failed G-d even though they did not have the law (Mosaic law). Much of it involved various forms of idolatry. The second chapter is about the Jews (and Paul was raised a Jew) and how they had failed G-d even though they did have the law. And, then in chapter three, we get to the point he is trying to make. In Roman 3:23, it reads:
23) For all have sinned, and come short of the glory of God.Paul goes on to explain that we are justified by faith and not by works or the "deeds of the law."
Now, let's return to Nero and Rome during this time. Rome had about a million people during this period, and about half of them were conquered peoples from different nations and cities. Many of those folks were sold into prostitution. Any Roman citizen could hire the services of a prostitute (male or female), and they did so (probably quite often). Prostitution was legal and big business (and, it was taxed as such). There were active and passive male prostitutes, and the passive male prostitutes were usually younger males and were castrated. The men (citizens) in Rome were allowed to use the services of the passive male prostitutes, and no one apparently batted an eye. They were also allowed to hire the services of the active male prostitutes, however that was pretty much frowned upon. Many did so anyway. With regard to the women, this verse does not say that they had sex with each other. It simply states that they participated in unnatural sex acts.
Nero had some pretty wild, crazy, distasteful, and destructive sexual impulses and habits himself. He had his first wife killed (beheaded), and gave her head to his second wife as a gift. His second wife came home late one day (from the games), and he kicked her in the stomach. She was pregnant at the time, and it killed her and the child. Well, apparently he was fond of his second wife, because he ran into a very young man (probably an adolescent boy) who reminded him of his second wife. He had the young man (or boy) castrated and he then married him. And, also he would put on animal skin clothing and go out and find people and tie them up to trees. He'd torture them and kill then apparently for fun and sexual pleasure (that's taking S & M a bit far, I think).
Rome was polytheistic (many gods) at the time. And, when they conquered another nation, they would generally just incorporate more gods and goddesses into their religious institutions and practices. Some of them were fertility gods and goddesses, so that was all part of this prostitution business going on at the time.
This is some of what Paul saw (and/or heard about since he wrote Romans from Corinth) going on in Rome, and he was trying to tell the new Christians there to avoid these things.
Now, let's go back to the passage in question. Verse 26 starts out with the phrase "For this cause." The question arises as to what cause Paul is referring to. To understand that we have to look to the preceding verses (this is the problem with proof texting scripture). Those verses are about how various past (gentile) cultures committed idolatry (of various kinds) and worshipped pagan gods while they should have known better. So, then Paul begins to discuss another type of idolatry ... temple prostitution and sexual obsessions and abuses of all kinds. And, he admits that he finds these things vile and unnatural. We don't really know what he meant by "natural use" here. Natural law (as described by the RCC) had not come into existence yet, so he may have meant what most often happens. Paul's audience in Rome was (overwhelmingly) heterosexual. They exchanged their natural use or desires to do unnatural acts (for them). It is natural for homosexuals to have same sex sex. But, it is not natural for heterosexuals to have same sex sex. It bears mentioning that many of these folks were also already married, and still participating in these activities.
So, was Paul talking to or about loving and committed same sex couples here? Most likely not. Was he talking about the sex that these couples have as an expression of their love for one another? Again, most likely not. That was not what he was looking at in Rome at the time or what his (life) experience had shown him.