There's one thing missing — an em-dash.
Em-dash is used specifically in place of omitted text, to introduce a small pause and designate the omission.
...a belief system which was true to him, and he — to it.
Reads differently, doesn't it? No longer does it look like a piece got lost somewhere, like some weird grammar. The em-dash marks the omission, clarifies the sense and breaks the flow, so that in speech (or verbalized reading) this sounds natural.
Now, what it means:
...a belief system which was true to him, and he [was true] to it.
— He believed that the belief system was true (as in not containing falsehoods)
— He acted "true to the system," that is, adhered to its rules - didn't try to game it.
Now, while the above might seem trivial to you, let me give you some examples where the two are not true:
- Most of higher-ups of the Party in Soviet Union believed Communism to be true.They believed the system would conquer the world and the inferior Capitalism would fall. Still, they'd take more than their fair share of the goods, owning good cars, good houses, being able to buy goods in shops not available to the citizen - in effect, they were not true to the system which was true to them.
- A priest who lost faith, may hide the fact. The salary is good, the job is secure, he doesn't know any other jobs, and is afraid to leave the comfortable life. He doesn't believe in God anymore - the system is not true to him. But he still performs burials, weddings, masses, teaching others about God against his own belief; he is true to the system, despite the system not being true to him.
Now as for your other question, you attach things to other things. That's the most common preposition used with "attach", nothing weird here.