Well, I don't know about ILIs, but I've been observing my IEE and SLI friends skirting around each other for about a year now, and I can talk about the SLI.

With her he's a bit more emotionally expressive but not a lot, and it only really comes out when pretty much no one else is there, but I've noticed it. He's still very curt and to the point, and his humor consists of dry jokes that more often than not are kind of making fun of her a bit, but it's because he feels secure in their relationship enough to do that - he's only started doing that with me recently, and not nearly as often lol. It's obvious he loves her romantically though because even though a lot of his behavior with his best friends and her will overlap, he used to and still does go above and beyond when it comes to actually, physically attaining or doing something that might help her do what she wants, be that driving her somewhere (he does this ALL the time) or helping her pick stuff out. He's extremely loyal, as Stance previously said, and he did this even after she told him she didn't want a serious relationship (they did get together recently, though).

I always find it funny, though, how me and him are never hesitant to call my friend out on her shit. Everyone else skirts around it. I guess that might be the way Fi is insensitive, my Fe friends tend to want to "set the mood" for a "talking to" lol. Which is like an intervention.