Should my fiancee justify his overpriced spurges on his children by pretending the objects are for ME?

I feel that my fiancee over-indulges his children - expensive gifts, vacations, expensives dinners out, etc. In order to justify the purchases he tells me they are actually for me - a 4 WHEEL ATV, a cell phone for an 11 year old, a high-end iPod, etc. His son was being for a Lobster dinner and he even later said that I did not appear to be thank ful for the elaborate dinner he arranged for me.
The main concern is that his children pressure me relentlessly during the pre-purchase stage - pick the blue one, shouldn't it have gold keys, etc. I become the middle man in the their game to convience Dad to buy - I feel used when he does and the kids feel resentment towards me if he doesn't.