I am in my first serious relationship... I don't really think my highschool boyfriends/girlfriends count as real dating, and I didn't really date anyone in college either, until the very end, and I'm still with him
Honestly, I don't really know. Since I started having sex, 5. Before that, 4 or 5? Long term though of those, I've only dated 3. And I've casually dated a couple others, but never relationships so I don't count those.