Do you find yourself acting differently in front of people of the opposite sex that you like?

So I have several example of people acting differently:

1.My best male friend is a bit of a player. He is lovely with me, always there when I need him, always caring, always supportive. But with his girlfriends he isn’t himself. Or at least not who he is with me. He doesn’t treat them well, isn’t considerate of their feelings.
2. The second I meet a guy that I like I become all wide eyed and bushy tailed. I’m strangely nice and accommodating and worst of all it seems to be completely beyond my control. I go strait back to being a fifteen year old on my first date. This seems normal, I know, we all want to make the people we love happy. However, I’ve never been the sort of person who just sits there and smiles blankly. I tend to be more hellfire and brimstone than house and white picket fence. (This doesn’t happen with every guy I date, just the ones I really like.)

So do you act differently in front of your S/O or potentials?
Why do people act differently with people they date?
Why is it so subconscious?