The female in a male-female romantic relationship. She provides love and emotional support for her boyfriend and is loved the same way in return. The girlfriend is also a friend, and thus is loved and respected on that level of relationship.
A girlfriend is not to be confused with a girl whom you date and find aggravating. If you view a girl as something just used for sex, or as the personification of a ball and chain, then the girl in question is not your girlfriend.
To conclude, a girlfriend is a girl with whom you love and with whom you enjoy spending time, and who feels the same way about you in return.
The boy spent the day with his girlfriend, having a very good time. As they are in love with each other, they were very disappointed when they had to part ways at the end of the day.
Sexual intercourse where there are only two participants. In addition, the participants are trying to give the other person pleasure and are placing that goal above the realization of their own pleasure. For example, when a man makes love to a woman, he is trying to get her to orgasm as opposed to trying to orgasm himself.
The boy was making love to the girl tenderly, trying to bring her pleasure.