Johnny Galecki has had quite a career, starting out in the late '80s with a starring role in "Christmas Vacation." From there, he found a recurring part on "Roseanne." Suddenly, he was a sitcom star, growing up as a teenager in living rooms across the country as the quirky but endearing David Healy, the boyfriend of Darlene Conner (Sara Gilbert). Galecki is probably best known these days for "The Big Bang Theory," where he was infamous for breaking others on the set . There, he played Leonard, who winds up marrying his good friend Penny (Kaley Cuoco).

Between "Roseanne" and "The Big Bang Theory" alone, Galecki has nearly two decades as a sitcom superstar — and on both shows, he wound up dating his romantic co-star. It hasn't always been happiness and on-screen love affairs for Galecki, ho

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