Money. Tis said money cannot buy happiness, but I would answer that by saying it can buy anything and everything conducive to happiness (or at least contentment), provided you resist the addiction of billionaires who think there is no such thing as enough money. If you cannot be happy rich, you got zero chance to be happy poor.
Wives will love you for however long they choose to, then dump you, and rob you blind in divorce court. Kids will demand your time and money, grow up, and either move off or take up squatters rights in your basement. If the former, you will see them rarely, and probably only when they want money. If the latter, they will parasitize you til evicted from the basement, or until you die, or until they stick you in a senior facility and sell your house. If lonely, do yourself a favor, get a pet, and spend your money on it. Wives and kiddies are a money pit that takes way more than it gives.