[Elmo]

To sound cheesy for a bit if I may, love doesn't always happen when it is 'allowed'. Unlikely, divide-crossing couples happen all the time in real life. Doesn't mean that there will be a happy ending, like in the case of Mithrellas and Imrahil but I think Tolkien tries to show how it can occur in the most unlikely circumstances and can break down logic and good sense.

Aegnor and Andreth are another example of a doomed romance that didn't contribute greatly to the cause of Arda. Tolkien believed in free will that the Maker would give His children. Love between elf and man should be included in this.