He's a fuckboy or What?

So here's the thing my close friend Jackie has a crush on a guy. She has had a crush on him for three years. But that's not the point intended, he liked her too the whole time, she would tell me that he always stared at her in class but she'd act like she didn't see him...At first I didnt believe her until I saw it with my own eyes. He would try to talk to her but Jackie of course was bad with guys which is crazy because she is so pretty. Everytime I would ask her why won't you just show interest. I'm telling you she was just stupid but that's not the point. This whole time they are recreating the same thing and sometimes bickering, but he's dating other girls and she would be so confused and know we are in our in our senior year and she has got a lot going on and she still likes him. I find out he has a girl but he always hides her like in the cut (small corner/areas of the school) And I don't even know how to explain to her that she should stop liking him because Jackie was talking about his girlfriend (FYI she didn't know it was his girlfriend) asking me why she had a hickey on her neck. I just don't know what to say? Help me put this in the nicest way and to explain to her that their is no future between them and she needs to move on, plus she is the president of the school.