What ami said above is true from my own personal experiences/observation, but seems to be backed by many studies here even... I would add -
North Node/South Node contacts (only in close orb)
Eros - Psyche contacts (only in close orb)
Perhaps even Kaali(Parvati) and Shiva, Osiris to Isis, or even Adonis and Ishtar, and Baachus/Dionysus to Ariadne ---
Although with Ishtar to Adonis the "fatedness" may be shared or in a love triangle... and not forever, happily ever after... and with Ariadne to Baachus/Dionysus there is the point of one being born for someone, but having to endure many rejections first... But, with Isis and Osiris or the Hindu-Vedic couples... you have the cyclic soul mate pairings.
or so I believe... ^^;
Firstly check Axis points... those are definitely the most important... N/S and Vertex/E.Point(Anti-Vertex) !
orbs must be close though I believe... connections made to the node and to a personal planet of one or the other party is also extremely significant, and then it reflect back to the house that planet rules... other asteroids should be considered too afterwards.. usually in case o pre-destined events there is a synchronicity to be found...
I've had at least 5 of these types of relationships with partners, and many more with family and friends... it isn't so uncommon... but romantically, it is... I think the difference lies in the rest of the picture... you have to have multiple contacts to consider an intimate relationship "pre-destined" or "soul mate"-y by definition... by example... ^^;
there are many asteroids to look at for this sort of relationship too... you can substitute Hebe and Herakles/Alcide for Dionysus/Baachus and Ariadne... because in this case, Hebe was predestined for Herakles and vs/vs but Herakles had to suffer first before they were united... (which is the opposite of Ariadne and Baachus/Dionysus)... but continues with the reincarnation theme... Baachus was reincarnated... so too was Herakles... and both had predestined partners of God/Human lineage...
Anyway - I hope this is a bit helpful at least!!! ^^
sorry for rambling! <3