Yeah, when someone perceived as a dual type, there can be higher expactations towards that person. That's one of the pitfalls of socionics. Sounds like you are aware of it, at least.
Also, the fickleness in romance thing is something I hear alot of people complain about nowadays, I myself have had some negative experiences there with fickleness, but not from SLE specifically. Seems to be a byproduct of something of our age, not sure what, could be instant messanging maybe.