What is your impression of the romantic relationship described in the sonnet?
I believe that the romantic relationship being described is a true relationship, not based just on physical appearance, but compatibility and loyalty. Although there are many reasons I get this idea, the line that hits me the hardest is line 14, "I shall but love thee better after death." The speaker loves this person so much, that even after they pass away, the speaker will love them even more and miss their presence to the point of heart-break.
Hope this helps!