Meaning

It was the conflict between his level, doubting mind and his overflowing heart which left him resentful and confused. = He was resentful and confused because his mind had doubts while his heart had no doubts.

Does that help?

Yes. Thank you, Mister Micawber.

I want to know whether I can understand it this way:

Thinking critically he doubted her behaviour but at the same time at the bottom of his heart he felt she would not have betrayed him.

I don't know. You have supplied no context whatsoever indicating anything about a relationship.

Here it is, Mister Micawber.

These lines are 'Birth' by A J Cronin. The speaker is a doctor who thinks that marriage is a merely an idyllic state as he reflects on the unhappy marriages of his friends. His thoughts only get reaffirmed as he thinks of his lover Christine.

"He thought of Bramwell, foolishly devoted to a woman who deceived him sordidly, of Edward Page, bound to

HIs feelings do not relate to Christine directly.

Thinking critically he doubted the perfection of marriage but at the same time at the bottom of his heart (because he loved Christine) he felt that marriage could be perfect.

Hi Clive

I'm afaird I do not know whether his are popular here. 'Birth' is one of the stories in the supplementary reader for class XI. And that is how I came to read it.