if i get a performance intake for my car to increase horsepower, will that also declrease my gas millage?

Only if you have a heavy foot!

I have a CAI and i find it gave me abit more HP but also it makes the engine sound deeper

im with shocker,

at 3500 rpm, the intkake you car hear th eintake work, breath better if you like, the car gives a nice deep tone as it is doing this.

i felt some more power to be honest, can't say i noticed anything on the gas, i tend not to pay attention the gas when your looking for power/performance..

After you get through honking on the throttle, due to the increased intake sound, it will get the same or a tiny bit better mileage.