In sickness and in health. After nearly 44 years of marriage, Jay Leno was heartbroken when his 77-year-old wife, Mavis, was diagnosed with dementia. A source exclusively tells Closer The Tonight Show vet is taking his wedding vows seriously, doing his all to tend to and protect his wife. “Jay has been wonderful,” says the source. “He takes care of her. He gets her out of the house, which she seems to respond favorably to. It’s a difficult situation, as anyone can imagine.”

The 73-year-old also filed for a conservatorship in an L.A. court in order to set up a living trust to ensure Mavis has “managed assets” to cover future care if he predeceases her. (The couple, worth a reported $450 million, have no children.) “It seemed like the prudent thing to do,” says the source. And totally in character: After the pair, who met at the famed Comedy Store, began dating, he proposed by telling her he wanted her to be covered by his insurance!

He still has her covered. “Mavis was always Jay’s rock and now he must be hers,” says the source. “She’s been unable to handle day-to-day tasks.” While it’s unclear when she was diagnosed, Mavis has been experiencing symptoms for some time, like forgetting things and lapses in short-term memory. “To see her decline like this is tragic — she has her good and bad days — but Jay’s been wonderful,” says the source. “He vows to look after her so long as he has breath in his body. He won’t let her down.”