I found a workaround to actually get the "soulmate" status (I know that one can skip the aspiration milestone using a cheat).
Things that didn't work for me:
- Travelling
- Resetting the relationship using the cheat "modifyrelationship" (both for the friendship as well as for the romance panel, both at home as well as on a different location)
- Repairing the game
My workaround :
1. Open the cheat window (Ctrl + Shift + C) and type "testingcheats true"
2. You will need to get the ID of both sims first using following cheat:
sims.get_sim_id_by_name <yoursimfirstname> <yoursimlastname>
3. Delete their relationship using the cheat (they will become strangers)
relationship.destroy yoursimID targetsimID
4. You can rebuild their relationship using the relationship cheats:
modifyrelationship <yoursimFirst> <yoursimLast> <targetsimFirst> <targetsimLast> <(-)amount> <track>
Example for the friendhsip panel (adds 50 points):
modifyrelationship Jim Bob Jill Smith 50 Friendship_Main
Example for the romance panel (substracs 50 points):
modifyrelationship Jim Bob Jill Smith -50 Romance_Main
5. Type "testingcheats false"
Also (I don't know if this is relevant) both my sims were at home.
I don't use any mods or CC.
The cheats I used are listed and explained here: http://ts4news.com/cheats