an inspector calls

That would be Eric Birling.

Eric Birling met with Eva Smith on several occasions. They first met in a 'bar' - to say the least. Eric forced himself upon her the first time, admitting he did it because he was drunk and could not stop himself. Since then, they regularly slept together. All until Sheila breaks news to Eric that she is pregnant with his child. Eric doesn't know what to do and offers to marry her - out of sympathy and pity. He doesn't love her and he's got himself mixed up in a complex situation heeded by his drinking problem. Eva knows about this as we see when she later goes to Mrs Birling's charity. We observe here an outpouring of emotion as Eva explains her entire situation - where she outlines her 'partnership' with Eric and his drinking problem, whilst never actually naming him. I digress, but, allegedly, Sheila tells Eric that she doesn't want Eric to ruin his life for her. Again, as but a child, Eric doesn't know what to say. Birling ridicules Eric later saying Eric is "spoilt" and here, we are forced to agree, as usually, all his problems are solived by his father before they even become problems. So Eric offers Eva (or Sarah to Eric) money and she accepts it. Well, until she finds out he has been stealing the money from clients of his father's company. Again, evidence of Eric being but a child in an adult's world - resorting to his father's company as opposed to sourcing the money legally and morally on his own - after all this is his mess. Sarah tells Eric not to come near her again, knowing that a relationship between them would never work. A summary of the reasons why include:

1. Eric doesn't love her, he is only using her for his own pleasure.

2. A marriage between the two very different classes would be very hard to maintain or even start.

3. She didn't want to be married to a thief - who knowingly would? Very few.

4. Eric is too young and weak to face the responsibilites of being a father - evidence of this found throught the play.

5. Eva didn't want to marry Eric because of his alcohol addiction.

I reccomend watching the BBC's 2015 adaptation of An Inspector Calls, if you haven't already.

Hope I was of help and was able to develop your knowledge of the play a little further.