I am taking significant other as someone you are exclusive with...I wouldn't be able to remember anyone I got naked, yet alone had at least one date with.
around 17-18 about a year and a half
the rest are lived with time:
~20 total of 5 years almost, married
26 about 2 years
28 about 2 years, engaged and broke up near the end, once the engagement happened she started trying to call the shots.
30ish about 3 months, don't know if we ever agreed to be exclusive
married again about 2 years now
between each except for about 2 years after my divorce where I only was with a couple chicks, I was pretty much on dates / ? weekly.