Hey IZ, you should ask CharmedJustice. She has been married to an ISTJ for several years. She might have changed her type to ENFJ but should give you insights...not sure she is still on.
I have an ISTJ friend and we get along very well, much more steady than some of her other friendship. Basically accepting who the other is at their core and letting things slide more or less goes a long way. You basically have to accept that this person will do XYZ for the rest of their lives - can you accept that? I think in romantic relationships there is often less give and take and more expectations because everything is just more high-pressure. You may SAY you can 'put up with' something forever but you know you really can't and you can't give up the idea that the other person should change for you "if they really love you" and then things get ugly.
I think for relationships particularly 'opposites attract' that's what both partners need to make it work - a lot of give and take.
Also, I have noticed with my ISTJ friend when it comes to dating is that people assume she is a very stable person so they try to set her up with other very stable (SJ-ish) people. She said she was almost insulted basically because she wondered if people thought of her as boring or why they thought she would want someone who basically is not exciting. You know like the house of hufflepuffs or whatever their name is in Harry Potter? That's how she thinks other people see her when it comes to dating, or at least when it comes to setting her up with other people.
Not sure if that answers your OP at all...