That Time of Year

So, I may be completely wrong, but i felt like the overarching theme in this poem was love. The speaker in this poem describes the changes outside as the seasons change as well as the changes outside when night comes. I felt that these two things symbolized distance or separation. I got this impression after I read the poem through once and read the final lines "This thou perceivest, which makes thy love more strong, To love that well which thou must leave ere long". To me this meant that- like in the changing of the seasons and daytime- we miss what we had before. The desire and appreciation of something always seems stronger once you have to go without it. To me it's like when the summer fades to fall and fall fades to winter all I can think about is summer and how much I miss it. It's from that separation that my appreciation of summer is strengthened. I feel like the whole meaning of the poem is summed up in those last couple lines. I could be really off, but that's just how I interpreted it.