Study the information about to and preposition + -ing.
1. Compare: afraid to and afraid of doing.
I am afraid to do something = I don’t want to do it because it is dangerous or the result could be bad.
People are afraid to walk here.
Jane was afraid to tell her parents about a bad mark.
I am afraid of something happening = it is possible that something bad will happen.
The path was icy, so they walked carefully. They were afraid of falling.
2. Interested in doing and interested to do.
I am interested in doing something = I am thinking of doing it, I would like to do it.
I tried to sell my car, but nobody was interested in buying it.
We use interested to when we want to say how somebody reacts to what they hear/see/read/know/find/learn.
I would be interested to know what he thinks.
3. Sorry to do and sorry for/about doing
Sorry to is used when we regret something that happens.
I was sorry to hear that Sam lost his passport.
Sorry to can be used when we apologise at the time we do something.
I am sorry to phone you so late, but I need your help.
Sorry for/sorry about doing something to apologise for something you did before.
He is sorry for shouting at you last time.
4. Remember these structures:
Want to do
Fail to do
Allow somebody to do
Think of doing
Succeed in doing
Prevent somebody from doing
Stop somebody from doing