As discussed under Mosiah 18:10 and 18:11, the original text had examples of plural desires acting as subject predicate following a singular subject and an associated singular form of the be verb (such as “it was”). Here in Alma 11:25, scribe 2 of 𝓟 initially wrote “it was only thy desire”, which is what one expects in modern English. But then virtually immediately scribe 2 corrected the singular desire to the plural desires (his s, inserted inline, shows no change in the level of ink flow). The 1830 typesetter, on the other hand, reverted to the expected singular desire. The critical text will restore the plural desires since there are other examples in the text of this particular usage.
Summary: Restore in Alma 11:25 the plural desires, the corrected reading in 𝓟: “and it was only thy desires that I should deny the true and living God”.