Billy Shake's Sonnet 73

I read Sonnet 73 by Billy Shakes and was not impressed. I'm not sure what message he is trying to put across, but I surely didn't quite understand it.
I would not recommend this to anyone. The English is hard to understand, and the poem doesn't have much to it. It's long and dreadfully carried on, not really leading to any climax...
The plot would appear to be about winter, and coldness- as Billy describes the trees as they are withering during winter and the fading leaves dying from the fall. He talks about the trees 'youth', which I presume to be saplings, as dying beings lying on a deathbed as winter envelopes them.
At the end of the poem he says 'This thou perceivest, which makes thy love more strong,
To love that well which thou must