Leading someone on

To use someone for love or manipulate their feelings for attention or other selfish reasons.

To persuade someone into believing something is not true. Most of the time, Love, attention, money or other things are the reason.

In some cases, the person who is leading the other on might be in a relationship. That is twice as bad. I am sorry.

Gabe: "Alexander was leading Katrina on for months and she didn't even know!"
Alexander: "I was bored. I have a girlfriend already."
Helen: "Oh wow-"

Adrian: "Leading someone on is such a terrible thing to do. What's wrong with you?"