It doesn't matter whether you're the General in charge of a military operation, the CEO of a multinational corporation, or the leader of a project team. This is your show and the buck stops with you.
If you're an enlightened, transformational leader - and I hope you are! - then you will have been encouraging your people to participate in planning and decision making and other aspects of management. You'll trust, motivate, encourage and support your people and you'll operate on the principle that if your people have a problem then they will fix it, and only if they can't fix it will they bring it to you. Even then, they'll also bring you at least one potential solution.
This is all well and good and lets your people feel empowered to be creative and to get on with the work. Ultimately, though, it is still your role - yours and only yours - to make the hard, unambiguous decisions that will have an impact on the fate of your organization. Your willingness to accept this role is the essence of leadership.
Do not flinch from this responsibility.
Even as you create an informal, open, collaborative corporate culture, prepare to be lonely.