What, may it be that even in heavenly place That busy archer his sharp arrows tries? (3-4)
Love sure does hurt. Cupid shooting arrows that are "sharp"? Since when has being shot by something sharp that's going fifty miles an hour ever felt good? Okay, sometimes love feels good, but in this poem it hurts a lot.
Sure, if that long with love-acquainted eyes Can judge of love, thou feel'st a lover's case; (5-6)
Love is a case. This makes us think of it as a mystery ("the detective is on the case"), or as something that is potentially harmful, like when we say "you have a case of the Mondays," or you have "a case of the chicken pox." The point is the speaker doesn't say "lover's joy" or anything like that.
I read it in thy looks; thy languisht grace To me that feel the like, thy state descries. (7-8)
Here we see that love has the power to change the way we look and move. The moon's "languisht grace" (his "sad steps," perhaps) and his "looks" (a "wan" face) make that pretty clear.
Then, even of fellowship, O Moon, tell me, Is constant love deemed there but want of wit? (9-10)
The first sign of the speaker's plight is evident here. He implies that Stella, his beloved, sees his "constant love" as a lack of intelligence, a sign that he's an imbecile or a joke. Stella sure sounds like a mistress of pain here.
Do they above love to be loved, and yet Those lovers scorn whom that love doth possess? (12-13)
Clearly, Stella is all about being loved but not loving in return. Love is only a one way street, and this really irritates Astrophel. This partly accounts for his feelings of sadness and pain.