Tin Nguyen spent Tuesday with her boyfriend Haisan Trinh celebrating his 32nd birthday. She had a surprise planned for him on Thursday. Together nearly six years, the couple had been talking marriage – Trinh had even been saving to buy an engagement ring – but the kind and generous Nguyen was already like part of the family, said Trinh’s brother Haian Trinh, 33. She was Haisan Trinh’s “first girlfriend, ever,” his brother said Friday as…