Did you fall head over heels for your partner or was it something that took it's time and developed slowly???
I didn't even know we were really getting into a relationship at first, we met online, we arranged to meet in person, and it all happened so fast

It started out with intentions of friendship from my side of things anyway, that's all I really expected, but I quickly fell head over heels.
What made you fall head over heels?
Maycontainnuts had it dead on: communication, compatibility, and chemistry.
The longer answer for me though is that nothing "made" it happen, it's sort of strange to think about it in that regard. Falling for someone just... happens

It's like asking why I love him, I can't really answer because the answer is truly a very personal and complex answer.
In general, he was simply perfect for me. I was attracted to him physically and mentally (which is so important to me because most of the people I've met that were mentally compatible with me have been unattractive to me, and everyone attractive has had the personality of a doorknob

It can't be one or the other as far as I'm concerned, it has to be both), we had many a common interest but also he
compliments me in so many areas that he has but I do not and vice versa (ie: we're not the same in those areas, but we work well together because of the differences).
To me, "falling head over heels" either happens, or it doesn't, nothing really makes or breaks it. It exists, or it doesn't.
What does "falling head over heels" mean to you (how does that show up in the relationship and in your feelings?)?
Passion. The "falling head over heels" idea equates to passion in my mind, not necessarily physical passion don't get me wrong here, I'm talking about... enthusiasm I guess is the correct word for it

Pure enthusiasm and passion and adoration for the relationship and for the person I'm with in all possible ways. The amazing feeling of knowing you would do absolutely, positively anything for that person in your life, and knowing they would do the same for you.