Deflated

I don't know whether I am doing this to myself but the situation at work has me feeling quite deflated.
On the one hand I should be happy and grateful that I have a job, given the current conditions, and one that I enjoy. But I'm starting to believe I'm being told one thing by the boss while he does the opposite.
I was told recently that I'm relied upon because of my knowledge of the field we work in, knowledge that no-one else in the team has. Yet I'm not allowed proper input into the content and direction of things.
I was told a while back that I would be able to take on a higher role one day. Yet whenever I try to take steps towards that I'm knocked back.
It's hard to know whether I can trust what I'm being told anymore. There's a chance I could get asked to go back to my previous job in he near future but that's something I'm not entirely sure I'm ready for yet.