Possible Clues:

• So engaged by Simon Gray
• If not love, the wires may have got crossed
• Failing that mother wisely comprehends
• Apart from that alternative, it's not stupid
• Starts letter back to her being clever in other respects
• Differently
• He swore it might be different
• Prudent to support unmarried mother in a different way?
• Mother wisely included it — or else!
• Returning to that woman's sensible -- or else!