Brakes, Maybe suspension Problem

assuming it tracks straight when brakes are not applied, one could assume that either the left caliper is dragging, or the right one is not operating properly.
im no expert, but id bleed each one. then check them for operation. hard to do. might just want to swap in new front lines and calipers. dont want to play games with brakes.
just one of those things, IMHO, that you need to examine. hard to tell you from a keyboard what to check. hopefully others will have some ideas.
good luck.

Jack one front wheel off the ground, check for free-play in the ball-joints and tie-rod ends by trying to move the wheel assembly fore-and-aft and side-to-side. If you pass this test then I'd give each brake caliper a closer look.