The real answer is in the timing (dasha)
Vedic astrology times everything through the Vimshottari dasha — the planetary periods running your life right now. A relationship most often reopens when a period activates the 7th house (partnership), Venus (love), or the planet that ruled the original bond. If you are in a period that has moved on from those significations, the pull you feel is usually the past closing, not reopening. The honest answer to "when" comes from reading which period you are actually in.
Is the karma finished? (the Rahu-Ketu axis)
The lunar nodes show karmic relationships. Rahu in play around the 7th house can pull an old connection back with sudden, magnetic intensity — the "we keep finding our way back" pattern. Ketu, the node of release, does the opposite: it detaches and closes, and a Ketu-heavy period is often the chart quietly telling you the lesson is complete. Many people feel the difference before they can name it; the chart names it.
What it would actually take
Beyond your chart, a real reunion shows in the comparison of both charts (synastry) and in whether their chart is in a period that turns back toward you. A one-sided longing with no supporting timing in either chart is the chart being honest. None of this is fate you cannot move — but knowing whether the door is open changes what you do with the waiting.