If you leave your department/business/team for a month, will it survive? If your response to this question is along the lines of, ‘no, I can't go on leave, my team will not survive’, or ‘how will work get done without me?’, some assessment is needed. I see three key reasons why you may have answered, ‘no’ above.
1) As manager you have under invested in your team, meaning you tend to see them as drones to simply keep the ship going. Do not ask them to change course beyond a few degrees without a crash and do not ask them to sail a new ship without a lengthy transition period during which you should expect some to leave. They are simply drones as you're treated them as such. This tends to happen when you fail to share goals, delegate responsibility or identify leaders.
2) You feel insecure in your role and are in constant need of your boss’ (and employees) approval. Expectations of what success in your role is needed. A meeting with your boss (or better, first a self-meeting) should be set up to review, a) role clarification, b) short and medium terms goals and c) KPI clarification.
3) You do not understand what it means to be a manager or it is simply not a strength of yours. If this is the case, become that guru specialist and own that! Acknowledge your shortcomings and hire someone who; knows how to manage people. Who understands employee engagement, delegation and that correct succession planning needs to be put in place for a business to succeed long term.
In summary: If you cannot go on leave for a month, there is something wrong with your management style and elements you need to assess within your business.