be/fall head over heels in love
From Longman Dictionary of Contemporary Englishbe/fall head over heels in lovebe/fall head over heels in loveLOT/VERY MUCHto love or suddenly start to love someone very much Sam was head over heels in love with his new bride. → headExamples from the Corpusbe/fall head over heels in love• It wasn't just the usual liaison: the two of them fell head over heels in love.