If you are co-buyers and co-owners, there is no gifting happening. A gift might occur when you sell the house, if you don't split the proceeds in the same way as you split the purchase, but that is something to worry about later. Even then, gift taxes are almost never owed in the US. Although gifts larger than $15,000 per person per year must be reported, gift tax is not actually owed until the lifetime total of gifts given is more than $11 million.
