Serious topic advice about exes?!?!?

So I have this friend, who dated her ex for 2 years but it was On-again off-again. Aside from that, they have been good friends 6 months prior to when they first began to date.

After their first breakup, he nicely said he wanted to be friends and hugged her. So they continued their friendship....... One year later, they realized they still liked each other and got back together. This only lasted for about 3 months.

After their final breakup (in 2012). They still remained friends and got along very well. Their relationship had no serous drama. He just wasn't ready for a serious relationship apparently.

However, my friend to this day, still loves and cares about him, but is afraid to tell him this (4 years since the last breakup). out of all the guys that she dated/ liked, she claims this is the first guy, she truly had strong feelings for and loved to death. They still get along well and occasionally, he still tries to flirt with her a little, so she is very confused.

This guy btw is super sweet, funny, outgoing, and apparently "brings her out of her shell"( she used to be shy). She has no idea how to admit to her ex she still loves him. What should she do?

Any advice. Only serious answers please!!!!!!!!!!!!