If someone takes citalopram for 3 years, will it take longer for it to clear your system compared to someone who took it once?

For your intent, yes: It would not be exactly an issue of 'clearing your system' as in half-life - but it will take more attention to tapering off to avoid certain risks associated w/ serotonin syndrome, etc. Discuss your concerns w/ our Dr - it's a good way to get to know a bit about their thinking on these matters and you can consider seeking one who fits you best.- perhaps a specialist..