What does the poem 'Her Song' by Thomas Hardy mean?

It's a poem about a young man in a happy relationship with a girl, who has a tendency to take it for granted too much and not consider the consequences for their relationship if he doesn't make more of an active effort to maintain it.

Eventually, a foreign guy turns up on the scene and he loses his girlfriend to him-the foreigner takes her back to live with him in his home country, and the young man is left to rue his loss, regretting not having valued his lover more when they were together, and considering that it's ironic that at night time, both he and his love-rival might have the same stars in the sky shining on them, even though they are thousands of miles apart.