When we pray to not be led into temptation but to be delivered from evil, I think we are asking to be kept from the opportunity that would draw us into sin. At the point where sin is our hearts desire then we have sinned. That sin unaddressed will inevitably lead to outward action.
Homosexual desire is itself a sin. It is the seed that becomes the act.
I agree that the desireeven the thoughtis the seed for the act. As a man thinks in his heart, so is he, the proverb says.
However, I do not pretend to know exactly when one crosses over the line from temptation to sin. I do know that it is not easy to resist temptation. Indeed, Jesus likened it to carrying a cross:
And he said to them all, If any man will come after me, let him deny himself, and take up his cross daily, and follow me. (Luke 9:23)
There are those who would say, "Deny yourself nothing; you do not have to carry that burden." The Church rejects that message.
I think the LDS Church's message to homosexuals is the correct one: We do not know why someone might be disposed to this temptation, but we know that to yield to that temptation is sinful and self-destructive. You must resist. Although it will not be easy, with God's help you can overcome.
The Church reminds the rest of us that we are all subjected to temptation. None of us has room to condemn others simply because their weaknesses are different from our own.