The first step to moving on is letting go.
However the reality is it takes time for most folks to get to a point where they decide they (really) want to let go and move on.
This is especially true if they did not want the relationship to end. Oftentimes they'll invest time and energy trying to win back their ex or beat themselves up for ignoring "red flags", or worse yet they'll "romanticize the past" and convince themselves that their ex was their "soul-mate".
In order for her/him to have been "the one" they would have had to see you as being "the one". At the very least a "soul-mate" is someone who actually wants to be with you! (And vice versa)
If someone breaks up with you they're saying:
"You're not (the one) for me!"
Therefore (acceptance) that it is over is the first step to letting go!
Secondly disconnecting from them is very important for the first 6-12 months of the breakup. Forget about being "instant friends". Your ex is the last person capable of helping you get over them.
No one goes from being "red hot lovers" to "platonic friends" similar to siblings overnight. Most enduring friendships that happen after a breakup do so after both people have found new people to love. They may bump into each other after a large gap in time and decide to stay in touch to catch up with what each of them has been up to from time to time.
However early on it's best to unfriend them in Facebook, delete email addresses, phone numbers, remove any belongings and photos....etc
Focus on spending time with your friends, get back to interests and goals you may have ignored while in the relationship. As time goes on consider dating others or possibly using a reputable online dating site. There is also meetup.com which is a hobby groups site where people socialize in person as a group concerning various hobbies and interests (meditation, hiking, theatre goers, book clubs, singles mixers, dancing, writers, yoga..etc)
With each passing day the pain lessens as you focus on other aspects of your life. You can't get to second base if you insist on keeping one foot on first. Once again you have to "let go" in order to "move on".
Thankfully there are over 7 Billion people on this planet! Odds are in everyone's favor that there is more than a few people who would be ideal partners for each of us. That person you feel you can't live without just know there are billions of us who do it every day!
(And you use to be one of us!)