they often adopt the attitude of: "if you tell me what this relationship is, I'll try to act accordingly" and then proceed to follow your lead. It's really funny and cute.
for example, if I openly proclaim that we're friends (whether with a male or female), they suddenly start acting like one. But if I drift off and don't show them anything one way or the other, they're kind of lost and don't know what to do. It's like they'll assume you don't want them unless you show interest and define it for them with creative Fe. Even SLE women are like this!
They also don't usually SAY they're sorry, but they will SHOW that they're sorry by chatting you up and being more playful than usual and initiating contact. It's their way of making sure things are okay. If they think they've hurt you, and they care about you, they genuinely feel bad about it but sometimes don't realize the damage they did until after it's over. I think this pains them a bit but they're so glad to be easily forgiven, as most IEIs are able to do.
I can see why these dual relations can be difficult to start because often, the SLE will charge in quickly and the IEI will stand back, unsure. SLEs are fast and action-oriented (no brakes) whereas IEIs (can be) more thoughtful and reticent which can sometimes leave them behind in the dust or leave the SLE questioning what's wrong and why the IEI is being so difficult or unsure of themselves.
of course this has all been said before. but it's interesting to watch it play out among various people I know.