Our Zimmerman sources say ... here's how it really went down:
Early this month, George made it clear to Samantha he was leaving her and leaving Florida. Samantha then dropped a bombshell-- that she was 6 weeks pregnant. George now believes she was lying about it in order to keep him in her grip.
George then offered to make a child custody and support deal ... but Samantha wanted him.
On Monday ... things came to a head when George was packing his bags to leave and our sources say Samantha concocted the whole gun scenario as revenge.