Take it outside ASAP and keep it outside until it is better.
Buddhist pine, aka podocarpus sp, is a conifer, and like most conifers, it hates being an indoors bonsai. In fact, a lot of bonsai enthusiasts will tell you that indoor bonsai is a misnomer, and that there is no such thing. Remember, the natural habitat of a tree is outdoors.
I suspect its either over or underwatering combined with being indoors that is killing your plant. Take it outdoors, and fix your watering. Watering is surprisingly difficult to get right, but is essential. First, take it outside, and then pour enough water into the pot so that it is streaming out the bottom. Wait a minute, and check how damp the soil is. If there is still water at the top of the pot, your drainage is too poor and that is killing your plant. If the soil is damp but not waterlogged, that is fine. Wait until the soil feels dry-ish on the top, and then repeat. In the US summer, that could be a day or two.
Some people water their plants by immersing them in a bath of water and waiting until the air bubbles stop.