These two sonnets may indeed be addressed to the "dark lady" of his sonnet, and yes she seems to be his lover, However, 130 is much more complimentary and focuses on the mistress' beauty. The use of the similes to compare her various physical features to some natural occurrences helps us to understand how rare he thinks their love is because she is so beautiful. On the other hand, 138 is somewhat negative and uses the word "lie" to do what shakespeare does best, play on words (i.e the use of pun). She lies to him and he knows it, but he listens anyway and ultimately they "lie" together.
