The way it works is simple, you have an INFP. You need at least one thing to relate between others. Whether you actually are the same or not, doesn't matter.
This is because of the way I perceive relationships working, both parties must agree on things, but for you both to be the same person would be... Weird. I could see that leading to lots of problems, due to how I've seen people interact with "themselves". Such as the INTJs I know. They both called each other crazy over at the lunch table, and the more violent one made a mess when the other one pushed a plate of food at him. It is a weird lunch.
I also believe I sit next to another INFP in class. This is because we both were the last to sit down and pick a partner. If he is not INFP, then he is ISFP.
As such, potential matches based on this theory, in order of greatest to least, are ENTJ, ESTP, ESFJ, and finally, ISTJ.
There are a hundred billion reasons why I would not have a relationship with ISTJ, but then again, look at Isabel Myers.
ESFJ I don't know enough about. Sorry.
But yeah. This is only a theory. I'm looking at what I think would rationally happen. Not what I think should happen or anything like that. Depends on a whole lot more than type for a relationship to work out. But yeah, in conclusion, it doesn't fit with my theory. Thus I am interested to see what happens.
I should create a spreadsheet on type vs. type relationships on Google docs that people can fill in themselves. That would be interesting.