The happy ending is that Sandler finds a way to make Barrymore love him over the long term. He makes a videotape that recaps the beauty that is their life together -- the proposal, their wedding, their daughter's first steps -- and she just watches it every morning to catch up. And he's even found a way to keep living his dream as a marine biologist, taking his bride out on a yacht on a tour through the Arctic, because for some reason that makes the most sense for a man whose wife suffers from a debilitating mental disorder.
So What's the Problem?
Just look at this shot from the film, after Barrymore finds herself in the middle of the goddamn ocean:
This happens every fucking morning. The last thing she remembers, she's a teenager living in Hawaii. She goes to sleep and wakes up on a boat, in the Arctic, with a videotape laying on her bed. Isn't this how all of the Saw victims wake up?
She then spends every morning reliving her accident and composing herself to meet her husband and daughter, who are complete strangers. And she's adrift among the polar ice caps, so there's absolutely nothing familiar anywhere near her. It's amazing she doesn't die of shock every morning.
On the plus side, she never has to know about Bulletproof.
And yes, we said "daughter." They have a kid at some point. Imagine waking up and finding yourself nine months pregnant with a sticky note on the VCR in a stranger's handwriting that says, "Good Morning, Lucy." Imagine her terrified confusion every time this strange infant wakes her up crying in the middle of the night. Or any time Barrymore accidentally falls asleep while her daughter is napping. Or, you know, the hilarious night she spent going into labor, completely clueless as to how the hell she got pregnant in the first place. You go to sleep as a care-free teenager, you wake up in labor.
"I cannot be held responsible for my actions if I just freak out and throw you to the sharks."