Deception, Lies and Snapes' big mistake

James Potter is alive, married to Snape and has lots of little kids! How is Lily involved? Why has Snape really not told James about Harry living with the Dursleys? Why is Voldermort sending Harry weird letters? And why is Sirius getting jealous Harry is starting to think it would be better of he just left the country! H/V J/S bad Dumbledore