a heartthrob
someone famous who is very attractive
Elvis Presley was a real heartthrob to millions in the 1950s.

a bleeding heart
someone who shows too much sympathy (usually said to show you disapprove of their sympathy)
Those bleeding heart socialists want to spend my taxes giving money to the unemployed.

to break someone's heart
1. to make someone who loves you very sad, usually by telling them you have stopped loving them and want to break up with them
She broke my heart when she ran off and married Mike.
2. to make someone feel very sad
It broke her heart when she didn't get into university.

to have a change of heart
to change how your think or feel about something
We were going to have a big party but he had a change of heart so we just had a few friends round instead.

Take heart
Said when you want to encourage someone who is feeling defeated or is about to give up
We've walked all day. Take heart, we're nearly there and we'll have a lovely meal when we finish.

to lose heart
to give up or stop trying to do something
They found the work too difficult and in the end, they lost heart.

to bare your heart
to tell someone your secret thoughts and feelings
Don't bare you heart to him! He'll tell everyone. He can't keep a secret.

from the bottom of your heart
very sincerely, very honestly
I promise to love you forever and I mean that from the bottom of my heart.

Cross my heart (and hope to die)
you say this to show that what you have just said or promised is completely true
I did see them and they were kissing! Cross my heart!

in your heart of hearts
what you think is true in your most secret thoughts
She said she didn't steal the money but in my heart of hearts I knew she was lying.

What's on your mind?
What are you worried about?

neglecting
not looking after something or someone that's your responsibility

to get back on the right track
to return to a way that will bring good results

to get over it
to feel better after something or someone has made you unhappy

to distract you from
to help you not to think about something unpleasant

not unless it's true
don't say something if it's not how you really feel or it isn't true (here, Professor Lewis means "Don't say that you're OK if you really aren't OK")