Building some support system sounds like good advice MarkK.
Is there any person among your friends (or family members) who could be supportive to you in all this?
Please be gentle as possible in ending so long relationship... I guess that is impossible to avoid some pain.
If it is possible write down those fears and share them as much as possible. You have to find way that suite you best in channeling them out. Some affirmative stance on all this could bring more positive perspective...
My story