Grammar & Prepositions

[allei]

Hello teachers! Kindly help me. I need some clarifications regarding these sentences.

Is it correct to say:
Sentence#1. He is very understanding to me.
2. He is very understading to my situation.
3. He is very understanding for my situation.

I'm confused because I used an automatic grammar checker, it says that the word understanding is the error. All the while, I thought the problem is the prepostion. I need an explanation so please help me.

Furthermore, is there any tip as to when and how to use prepositions to and for?

Thank you.

[Tdol]

He is very understanding of my situation.

[allei]

hi tdol,

thanks for the immediate reply.

need to know also what's the best way to determine wether a sentence is transitive verb or intransitive.