impossible to say. depends on how invested you were in the relationship, how long it lasted, why it ended, and what kind of person you are too. but you'll know when you're ready. give yourself all the time you need...

Dude for some people it takes like 20 minutes...
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I don't think there's any hard and fast set rules. Go out when you feel you're ready...

Its really hard to say exactly how long it takes but I really don't think how long you dated is that big of a factor. To me the break up is the key thing that tells you how long it will take. If it was mutual then I'm sure it wont take long, but if someone broke you heart it can take a long time. Sometimes I think you just have to put yourself out there again and test the waters, staying in a wallowing has a expiration date. Going out with family and friends and surrounding yourself with positive people speeds up the process and helps you get back on your feet!..