Firstly, in relations where money plays a major role such as business should involve truth.
This sentence is very confusing. First, you should pay lots of attention to your grammar. Then you need to be more cautious about clarity of your sentences. Express one idea in one sentence and make sure it is delivered to the reader very clearly. In this sentence, what should involve truth? Is it the relationship ? or business?
But it lastslasted for only six months.
... you did business together last year, so this sentence should be in past tense.
The main reason for its failure was he lied withto me regarding the profits.
This not only demolishesdestroyed our partnership but friendship too.
.... as dumi mentioned above, be very very careful about using synonyms. Don't use them if you are not sure of the word.