The relationship of Christ the Groom and the Church the Bride has to do with marriage. In fact it
is a marriage, the Marriage. Our marriages, when they resonate with the Marriage, point to it and prepare us to live in it. I'm a little hesitant to say that this is merely metaphorical, because then I'm fearful of treading on the slope where "is" becomes equivalent to "signifies" but not "equals." This becomes dangerous when we turn, for example, to look at what Christ means by "this is my body."
I'm indebted to my seminary advisor, Dr. Robert Jenson, for teaching me the insight that we cannot project or extrapolate from our human experience to the divine reality. Thus, God our Father is not like our fathers, only moreso. This kind of extrapolation seems benign when we have good fathers, but it is the move that some make when they say, "I knew my father to be abusive, therefore I cannot accept that God is our Father, because that makes him [well, probably, they would say "that makes God" and would avoid the pronoun] omnipotently abusive."
Having said all that, I would agree that metaphors can be stretched too far. I'd disagree on whether Groom–Bride talk is metaphorical. After, "the two shall become one flesh." This is true for the man and the woman here and now
because it shall be true of the Groom and the Bride in heaven.
And the key is to move from the Tradition's proclamation of Christ the Groom and the Church the Bride to an understanding of human marriage, rather than to extrapolate from notions of human marriage to fill out what we think it might mean for the Church to be Christ's Bride. This is analogous to not projecting human notions of fatherhood upon God the Father.
I seriously doubt that the image of Christ as the groom and the Church as the bride has anything to do with sex. It is about a close, intimate, and committed relationship.
Which only proves that metaphors are never exact matches for the thing which they attempt to describe. The fact that the metaphor of Christ as the groom and the Church as the bride doesn't refer to sexual intercourse does not prove that heterosexual intercourse isn't part of marriage. It only proves that the metaphor can't be stretched beyond what it meant to include other things not intended as part of the metaphor.