With my bereavement counsellor's hat on , yes it is a loss and you are grieving . There isn't any social norm on this one. No wedding party, no christening celebration to mark the start of something new or funeral to mark the end of a life, just a big empty chasm.
Whatever you are to each other now, you did love one another . You were a big presence in each others lives. You laughed, loved and maybe were sad together. Think of it as building little bridges from one person to another and now those bridges need to come down bit by bit.
It's a long slow process. It won't happen overnight. While you may not be 'in love ' with them anymore parts of you will still love that person for what they were to you and the good times you had. As its an amicable split no doubt you care very deeply for their welfare.
There's also just missing a physical presence. While you might feel relief that a difficult situation has come to a close we are programmed to recognise the familiar and to some extent miss that familiar presence. Even if times it annoyed the hell out of you!
Letting the grief out is an important part of the process as those bridges you built gradually slip away. The tears you shed are ancknowlegement of the love you once shared. Be proud of yourself for the lovely human being you are . For recognising something wasn't working and having the strength and courage to go it alone instead of letting it dissipate until resentment set in.
Gradually those numb feelings will recede as you start to pick up the new threads of your new life . New interests and new people will step forward into the new space you have created and maybe then you will be able to look back at your old relationship with a fondness that honours the good and let's the bad reabsorb into the mists of time.
That's how I feel about mine anyway.