The dagger is often used to commit a murder in literature, in particularly in Shakespeare’s tragedies. The dagger is a symbol of an act of violence, the dagger is analyzed in Freud's The interpretation of dreams, The murder is interpreted like a violent sexual act and the dagger symbolized  the instrument which you used to commit it. In addition the dagger causes a loss of blood and that happens in the first sexual act. So Shakespeare seems to have a negative opinion of sexual intercourse, also in Th’expense of spirit you can understand it indeed Shakespeare uses harsh sound and negative adjectives to connotes it ( for example perjured, murderous, bloody, full of blame, savage, extreme, rude, cruel..).