Judging from the context you provided, I can be pretty sure that it means _myself_.
{} could surely sometimes mean _oneself_ and sometimes _you_ , but their registers) are so different that we almost never confuse them in real settings. means _you_ in vulgar talks (or common in some dialect), and _oneself_ in elevated parlance.
In this case, it is clear that speaker is giving a formal, bookish line, not only in form but in matter. Thus it is only natural to be interpreted as _oneself_ , in this case, _myself_.
**PS**
Not knowing the plot, I'm not sure whether the means "belief" as in your translation, or "spirit", "soul", "super-ego" kind of thing (opposed to some demon or evil).
**PPS**
The translation of the second line:
>
should be literally like:
> The reason I came here is to restrain myself lest it loosen/waver.
The accurate interpretation of , , and is up to the context, though.