Great question! I grapple with that one myself. Don't know the answer, but here is one idea...
Assume we manifest our experiences according to all of our beliefs (the ones we really have, consciously and subconsciously).
Therefore, it may be possible to manifest many different relationship "truths." Each experience will seem absolutely true for the person having it. The person who believes that God chooses your best relationship, and who has no conflicting beliefs about self to interfere, will have an experience of God choosing their right mate. The person who believes that they are completely self-determining will experience that. Maybe "God" lets us have any experience we want (believe in). The person who has a combination of beliefs gets a mish-mash of experiences. We decide. Of course, in a relationship the other person decides too.
On the other hand...
perhaps we have a "higher self" who has made some decisions about what it wants to experience in life. We are the vehicle for that experience. Therefore, at any time, our higher self may arrange for a "wild card" experience to enter our lives (something our beliefs did not manifest, but something totally new), or may block certain things from happening. It certainly seems that way to me sometimes.
You can try to create what you want and let the chips fall where they may. If you do not create, you stagnate. If you move forward and create (choose) something, whether it gives you pleasure or pain, you will always learn a lot (about your REAL beliefs) and will be able to cross what you don't want off your list the next time. Refusing to choose is a way to try to avoid "mistakes" and the scary responsibility of free choice (no one to blame, no absolute wrong or right choice). Perhaps you can't mess up or choose wrongly. You can only choose, and then enjoy or not enjoy the experiences that follow. Does it really matter?? We are the creators, not our circumstances or experiences.
Other ideas or experiences??
