Remember the good and the bad times. A'lot of people will tell you to lock them away, well that's easier said than done. But if this person means so much then you cant just suddenly and easily cut them off this isn't a piece of string we are cutting off, we need to slowly cut off this thick cable. So to do this? look deep inside and look at the memories together, yes... its gonna hurt and it will be painful... But look at all the memories, the good ones, the bad ones, the times when you felt like everything came crashing down, the times you wish the impossible was real and maybe what if he wasn't married? Let your emotions flow cause this is what you want, let them flow out of you; cry, laugh, jump around LET YOURSELF GO!
Now that you're open and all these emotion are out there, take a pen/pencil and paper, yes paper and just write freely. Don't just skip this, the power of the written word has conquered and united kingdoms, the power of the written word is endless.
Now that you've written all of this ask yourself? are you blaming yourself or him? are you being bias? is this logical?
If you blamed yourself, ask yourself why? is it really your fault? or did all of this MAKE you think it was your fault? now list the good things you've done, when you're done look at what you've wrote and realize that you have no reason to blame yourself.
If you blamed him then list down everything bad or wrong that he has done, now look at that list and ask yourself why did you waste so much time on this? why did he take so much of your time for these reasons?
Now learn from your mistakes, learn what went wrong, what you've learned, we all make mistakes, the pain of this person leaving...just hurts... and that's okay.
Now take everything he has gotten you or anything that remind you of him and get rid of it! Slowly just say good bye to everything, maybe is was jewelry? and you're thinking oh its expensive I should keep it? but at the same time when you look at it you will think back of the memories you so wish to let go. This will hurt but you have to do this, you're walking away and getting closure. Tell your self that you're stronger for everything you get rid of that reminded you of him.
Enjoy being single. Every morning when you wake up, tell yourself how wonderful you are and how that it's a brand new day that is unfolding for YOU. Walk to your wardrobe and wear what you want to wear. Make yourself pretty and beautiful knowing that there are a lot of people out there waiting to admire you. Start to learn to love yourself. Meet up with friends who you've lost contact with during the relationship and make new friends.
You might still be tormented by memories of that person. It will be normal. But give yourself a timeline. It can be a week or a month or two but tell yourself when that day comes,that will be the day when you must stop wallowing in self pity and angst and start life anew.
You can do it!