What's your
definition of drift?
Less meetings means you see less of them. Physically, its
drifting.
But this doesn't equate
to emotional drifting. It only creates possible risk
channels of emotional drifting.
Relationship is best to upkeep with a minimum of once a week
(CloUdiSm suggestion) and whenever possible during extra/free time
if you both could. Anything less than that has negative effect,
though strong communication and other factors can prevent it.

P.S: There must be mutual effort to keep love going strong
regardless of the frequency of meet-ups.
Cheers