At times in life, we are faced with difficult choices and either we make them or someone else makes them for us. Three months ago, I would have said never to both Clinton and Trump but it is now down to those two and since I choose to participate, I will vote for the one who in my judgment will do the least damage. I respect your view but can't agree that this is a moral issue.
It is not down to two. There will be others on the ballot, and as unpopular as the two major candidates are, there's a fair chance of an alternative.
It has been my experience that endorsing that which I do not believe in *never* works out for the better. I respect your decision, and I truly hope you don't rue the day... But IMHO and experience, you will.