It does not have to be restricted to a man's penis entering a woman's vagina. The reason I'm being blunt about the definitions is that you stated that you and your girlfriend have engaged in foreplay, but you have been able to stop before thinking about sex.
By that, I must assume that you have engaged in activities that stimulate your sexual desires, but that you are stopping short of intercourse.
The human body is designed to complete the act of sex once sexual activity is engaged.
We tend to not only repeat the things that make us feel good, we often look to prolong the feeling.The problem is that repeated exposure dulls our sensitivity.It takes longer exposure or new things to fan the flames again.The greatest danger that the Corinthians faced was the thought that it can't or won't happen to me.When we take that attitude, then we become lazy in our fight against sin.What about the other drivers, pedestrians, animals, or mechanical breakdowns?The assumption is that you are always and fully in control, but the reality is that we can only control a small portion of our world."Foreplay" is defined to be those actions taken by a couple in the preliminary stages of a sexual relation to build up sexual passion.These actions would include kissing, touching, and caressing. For example, a kiss from your mother as you walk out the door, or holding hands as you stroll through the park with your girlfriend, or giving a friend you haven't seen in ages a warm hug are all done without any sexual connotation.I fear that we are rapidly heading down the same path, unless more people, like you, realize that what God wants ought to matter because God has our best interest in mind.I've noticed that people tend to play fast and loose with word definitions.