How does Macbeth feel in Act 1, Scene 7?

Macbeth is worried that killing Duncan is not a good idea, but Lady Macbeth talks him into it.

Macbeth was ready to kill Duncan when he found out he was not named the king’s heir.  He was feeling very ambitious, since the witches told him he would be king.  However, when he returned home he was suddenly not so ready.  Killing the king suddenly seems like not such a good idea.

Macbeth is worried about the consequences of killing the king.

If it were done when 'tis done, then 'twere well
It were done quickly: if the assassination
Could trammel up the consequence, and catch
With his surcease success; that but this blow
Might be the be-all and the end-all here,
But here, upon this bank and shoal of time,
We'ld jump the life to come. (Act 1, Scene 7)

He starts to sort of talk himself out of it.  He says in this soliloquy that Duncan is there at his castle “in double trust” because Macbeth is supposed to his loyal kinsman, and is also his host.  How can you kill your own kinsman, especially when he is visiting your house?  Macbeth points out that he should be protecting Duncan, not murdering him.  Duncan has been a good king.  He does not deserve to be killed.

When Lady Macbeth arrives, she doesn’t know what Macbeth’s problem is.  She tells him to be a man, and stop whining.  He is still worried about the risks, but she's not.

MACBETH

If we should fail?

LADY MACBETH

We fail!
But screw your courage to the sticking-place,
And we'll not fail. …(Act 1, Scene 7)

Macbeth is impressed with his wife’s resolve.  He agrees to do it, inspired by her fire.  He knows that she is a unique woman.  After all, what does he have to lose?  She laid out the entire plan.  All he has to do is follow it.