If you're dating someone, and I mean actually dating, you're just going out on a casual basis and having some fun.
It can be with whoever you want and you can go bowling, out to dinner, go see a movie, etc.
If you have different long-term goals – attitudes towards children or travel, for instance – it could cause serious heartache down the line.
The perfect way to further demonstrate your commitment is to introduce your significant other to your family and friends.
So if people are in a relationship, they are typically in love with each other and they want to spend their time together.