I've been a hard deterministic for my entire life. I just can't wrap my head around free will. Our brains are made up of chemical pathways, so all of our decisions/thoughts/behavior must be determined by biochemistry and genetics. Or they are determined by environment.
This may not be a satisfactory answer, but I see two ways of grappling with this.
1) MY IDEALIST ANSWER
Material reality does not really exist as such, only consciousness. However, consciousness effects consciousness; the thoughts of other beings, most importantly a Supreme Being, can greatly constrain your own consciousness' ability to reshape reality. Imagine playing tug of war against an elephant. So it is with consciousness; you may try to will yourself into believing that a certain thing is not so (my leg wasn't really cut off by that axe murderer), but some things, particularly those that exist outside of our own thoughts, would run up against the observations of many other living creatures and the overall design of God, and so without the direct intervention of God it would be impossible to make it budge one inch.
Objective reality is the system of logic that can, with the most internal consistency, reconcile the varying experiences of every observer; it can change, at least in small fashion in its boundaries, as people's observations change. Your actions are still your actions as they flowed out of your thoughts which come from your own stream of consciousness.
In this view, consciousness is not epiphenomena of material conditions so much as material reality is epiphenomena of consciousness.
2) MY MATERIALIST ANSWER
If you take a fully materialist view of the world, then your decisions are indeed all strictly determined by biochemistry. In the sense that if you knew the exact physical state of the brain at an instant you could predict the next action with 100% accuracy, and then the next one, and so on, and so in some sense it is all predetermined.
However, I think you might say that we would just as well accept or reject determinism for predetermined reasons. In the end, you have to ask what is useful, practical. I think that, in a way, there is a sort of suspension of disbelief that determinism requires, a faith in free will.
At the end of the day, no creature can really function off of a belief in its own determinism. No creature acts as though it buys into the idea. This, to me, suggests that the idea may just be fraudulent to begin with if our very being rejects it so much.