How is the theme of suicide explored in Macbeth?

The death of Lady Macbeth by her own hand is the play's sole suicide, but it is significant in that she is apparently unable to live with herself because of her role in the deaths of Duncan, the chamberlains, Banquo, and Macduff's family. Guilt consumes her immediately after Duncan's murder, and it no doubt weighs heavily on her conscience since she has urged Macbeth to commit it. Before Duncan's death, Macbeth expresses doubts about the regicide, telling his wife that Duncan is a good king who has recently shown his gratitude to Macbeth. That, and the fact that Duncan is a widely respected king, makes Macbeth hesitate until his wife calls his manhood into question if he fails to act.
Lady Macbeth's sleepwalking and the confessions that the doctor and the gentlewoman overhear are evidence of the extent to which she is troubled. At the point in the play where she commits suicide, her husband is acting independently of her, and she realizes that they are unlikely to remain the queen and king of Scotland. Macbeth's response to the news of her death is that she should have lived longer, but he quickly moves on to face whatever obstacles remain to him staying in power.

I'm not sure there's really enough discussion of suicide in the play to convey a theme in regards to it. However, Malcolm, the late King Duncan's heir, announces at the very end of the play that they believe Lady Macbeth to have, "by self and violent hands, / Took off her life" (5.8.83-84). In other words, they think that she killed herself.
We need not look too hard for answers why: at the beginning of act 5, Lady Macbeth exhibits some major guilt for the wrongs she and her husband have committed. For example, she says, "Here's the smell of the blood still. All the perfumes of Arabia will not sweeten this little hand" (5.1.53-54). She imagines that she can still see and smell Duncan's blood on her hands, and this seems to signify the terrible guilt that she lives with as a result of her part in his murder. Lady Macbeth also mentions Macduff's wife, lamenting, "The Thane of Fife had a wife. Where is she now? What, will these hands ne'er be clean?" (5.1.44-45)
She seems to know, then, that Macbeth ordered the murders of this innocent woman and her children, and she feels guilty about those deaths too. It is likely that the combination of her guilty conscience, inability to sleep, and emotional distance from everyone in her life including Macbeth, led to her suicide.