not doing the thing he did
Macbeth could have tried to seek guidance and counsel from trusted advisors or friends to help him navigate his ambitions. He could have also practiced self-reflection and restraint, understanding the consequences of his actions before committing to them. Furthermore, Macbeth could have focused on appreciating what he already had rather than constantly striving for more power and control.
Lady Macbeth
The line "what's done, is done" is spoken by Lady Macbeth in the play Macbeth.
Her part is decisive. If you read or watch Act 1 Scene 7 you will know that Macbeth, left on his own, decided not to commit the murder. He says "We shall proceed no further in this business." Lady Macbeth then proceeds to change his mind, at least for long enough that the deed gets done. She appeals to his irrational emotions, when his decision not to commit the murder was based on reason and logic, as shown in Macbeth's speech, "If it were done when 'tis done, then 'twere well it were done quickly."
the quotation from Shakespears Macbeth is "if it were done when 'tis done, then 'twer well it 'twer done quickly" (Macbeth, act 1 scene 7)
Drugged them.
I'm guessing that you are asking two questions: "How does Malcolm feel about Macbeth?" and "What has Macbeth done to become the king?" The answer to the second question is simple: Macbeth killed King Duncan in order to become king. The answer to the first question is almost as simple: Malcolm hates and fears Macbeth. I hope your command of English is sufficient to understand this answer.
SAY YES I DO CONSIDER MYSELF AN AMBITOUS PERSON HOWEVER IM MATURE ENOUGH NOT TO ALLOW MY AMBITIONS TO GET IN THE WAY OF THE JOB AT HAND. GETTING THE JOB DONE IS MY FIRST PRIORITY.
she talked him into killing the King by accusing Macbeth of being weak and cowardly
Her part is decisive. If you read or watch Act 1 Scene 7 you will know that Macbeth, left on his own, decided not to commit the murder. He says "We shall proceed no further in this business." Lady Macbeth then proceeds to change his mind, at least for long enough that the deed gets done. She appeals to his irrational emotions, when his decision not to commit the murder was based on reason and logic, as shown in Macbeth's speech, "If it were done when 'tis done, then 'twere well it were done quickly."
Lady Macbeth's statement "What is done is done" is ironic because she says it to try to reassure herself and her husband after Duncan's murder, when in reality, the consequences of their actions continue to haunt them throughout the play. The statement reflects Lady Macbeth's attempts to suppress her guilt and anxiety by dismissing the gravity of their crimes, which ultimately leads to their downfall.
After the banquet where Banquo's ghost appears, he tells Lady Macbeth that he "will send" so he hasn't done it yet. The next time we see him, he is visiting the witches, and then Lennox brings word that Macduff is fled to England. Macbeth says "Time, thou anticipat'st my dread exploits." What this means is that Macduff got away before Macbeth could get to him. It would seem that Macbeth never does send for Macduff.
The crucial part. Without Lady Macbeth, this would have been Macbeth's final decision: "We will proceed no further in this business." Macbeth would never have killed Duncan unless Lady Macbeth had goaded him into it.