"It's not the worst tragedy. But I really wish I had bought myself a man! A good man who would be a great father, I really do. I think it's a better way to go," the actress, 68, tells PEOPLE.
So what stopped her? "I think I was not practical," says the mother of two (daughter Dexter is 18, while son Duke is 13). "I had some insane idea that I had to be 'in love.' Now I see what it really takes: real consideration that you're a good team together."
The man she most wanted to make things work with was her Godfather costar and boyfriend of five years Al Pacino. "But he was even less inclined to be realistic than me. And I was on the cusp of being very old. So that poor guy. I don't think he was really that interested. And I don't think a long-term happy marriage would be easy for him."
Keaton – whose second memoir, Let's Just Say It Wasn't Pretty, hits shelves Tuesday – hasn't ruled out finding another relationship. "But I can't imagine it," she says. "You have to put yourself out there, and that's really hard for me. Always was."
She prefers hanging out with pals like Jack Nicholson and appreciating her "wall of men" (pictures she's collected of men she considers beautiful, including Sam Shepard, Jeremy Renner and – wait for it – Abraham Lincoln. "He was so romantic! Kind of hideous but not.")
And Keaton's not immune to the occasional crush from afar. "I just saw Louis CK on Saturday Night Live. Oh! How could anybody be that funny?" she tells PEOPLE. "I don't think he's beautiful, but I am in love with him."
For more from Keaton – one of PEOPLE's 50 Most Beautiful of 2014 – check out the latest issue, on newsstands Friday.