Juliet's suicide follows Romeo's. She awakes to find him dead, and then uses his dagger to end her own life. Obviously, Romeo and Juliet both have decided not to live without one another. Their suicides are prompted by the belief that both have lost the person they cherish...
Juliet's suicide follows Romeo's. She awakes to find him dead, and then uses his dagger to end her own life. Obviously, Romeo and Juliet both have decided not to live without one another. Their suicides are prompted by the belief that both have lost the person they cherish most in all the world, and both have contemplated suicide every time their plans come close to be thwarted throughout the play. However, Juliet likely sees herself as particularly without options at this point.
It must be remembered that Juliet first threatens suicide when she believes her parents will force her to marry Paris. To do so involves not only being untrue to Romeo but to break the rules of the Catholic Church. She never considers running away with Romeo without her parents believing she is dead because of her society's placing such importance on a girl's obedience to the wishes of her parents, particularly her father.
By the time she awakes in the tomb to find Romeo dead, Juliet is given an option by the panicked Friar Laurence: she can come away with him to a convent, either to become a nun herself or to allow herself to be cared for by the sisters ministering there (his specific meaning is not entirely clear). To become a nun would allow Juliet to remain out of the power of her family, but she would have to live a chaste and disciplined lifestyle. To be cared for by the nuns would give her some time out of her family's control, but it is more than likely that the Capulets would want to reclaim her. However, her reputation in Verona might be ruined as a result of her secret marriage and its connections to the deaths of Romeo and Paris, making it hard to find her another willing match.
In Juliet's mind, this is a no-win situation. She ends up rejecting the friar's offer and killing herself. Her calling the dagger that kills her "happy" signifies that to her, the only good scenario is the one in which she rejoins Romeo, even if that means rejoining him in death.