Why did Lily marry James ? / Snapes other worst memory

[davydarmstrong]

No: HPFGUIDX 66587

Lily married the arrogant James because she fell in love with James.

Because she drank the love potion that Snape prepared to make Lily 
fall in love with him (Snape).
There are several ways this could have happened:
1) by accident, she drank the potion (in her butterbeer?) and saw 
James before Snape, or the potion was prepared with one of James's 
hairs instead of one of Snapes
2) deliberately, James knew that Snape had prepared this potion (and 
why) and stole it from Snape and administered it to Lily because he 
wanted Lily to go out with him

This would be one of Snapes other 'worst memories' that he didn't 
want Harry to come across.