In Psalms 110:1 King David says, "The L-rd says to my L-rd..." How do you interpret David’s "L-rd" (my L-rd). Does King David have two "Lords"? The second "L-rd" seems to be describing Messiah.

There is only one G-d. Your question is based on a mistranslation. The second "lord" is -in Hebrew- not a word used for G-d, but one referring, even in modern day Hebrew, to a distinguished person (formal letters in Israel begin with the salutation: "Adonee Hanichbad"). The psalmist writes about Avraham or about David himself.