When I 'fall for' a person, it takes me a while to realise that this curious physical change that comes over me when they're around is due to a crush i.e. I crush 'subconciously' and it takes me a while to realise it.
The duration varies; may be anywhere from two weeks to half an year. As for their faults, I'm not particularly blind to them but at the same time I do give them more leeway than I would with other people.
The feeling is as much, if not more, physical than emotional and I get a surge of fire rushing through my body when I'm around them.
In a 'nutshell', Mozart sums it up best (no wonder they say he may have been ISFP):
I'll tell you what I'm feeling,
It's new for me, and I understand nothing.
I have a feeling, full of desire,
Which is by turns delightful and miserable.
I freeze and then feel my soul go up in flames,
Then in a moment I turn to ice.
I don't know how to hold it, nor even what it is!
I twitter and tremble without knowing why,
But still I rather enjoy languishing this way.