But Ruth replied, "Don't urge me to leave you or to turn back from you. Where you go I will go, and where you stay I will stay. Your people will be my people and your God my God. Where you die I will die, and there I will be buried. May the LORD deal with me, be it ever so severely, if anything but death separates you and me." (Ruth 1:16-17)
It's no wonder that the above passage is so frequently recited at weddings; Ruth's pledge to Naomi is one of the most powerful covenantal statements in the Bible. Even though I don't see any good reason to believe that there was anything sexual about Ruth and Naomi's relationship, it is nonetheless interesting to stop for a moment and ponder the fact that so many heterosexual couples are taking a promise spoken between two women and using it in a romantic (and sexual) context.
Ultimately it's only as big a deal as you choose to make of it, but I do wonder how many of those couples would have found a different biblical passage to use if that thought had ever occurred to them.