Quote Originally Posted by snoop View Post
It's not unusual in dreams where you try to have sex for you to more or less lose control of yourself because you're responding to dream input with one of your baser desires.
I second this. It is also important to note that if you were semi-lucid, as is common for beginners, often you notice you are dreaming and have some control but are easily distracted/pushed by the dream itself. Your comment about feeling like the dream was pushing you is pretty good evidence of this; it is likely you were lucid enough to know what was going on but not enough to fully resist the plot your dream had already lain out for you. Now, why you would have a dream like this in the first place has something to do with the current state of your psychology... if I had to guess, a mix of your buried feelings for this girl and fear of becoming what her dad despises, as others here have said.

Please remember that dreams are yours. You can't hurt anyone inside them. Lucid dreams are meant for exploration, and fantasies are part of that exploration. Just be careful not to hurt yourself emotionally!