Help me with my Dad please!?

Okay, so my dad always promises to take me on trips, and he never ends up keeping his promises- he never even bought me a birthday present for my birthday a MONTH ago. He owns his own business and is involved with stocks and has a LOT of money, and he spends so much on his girlfriend, like he buys her 500$ Tiffany jewelry, and they go shopping almost every week- but when i ask him for a pair of 15$ sweatpants, and he says NO. My parents are divorced, and my moms disgusted with how he's neglecting me, and i just dont know what to do. He always breaks him promises, for example I bought a 500$ Nikon camera on sale, then he told me the camera i bought wasn't good and he said he was gonna give me his 1000$ Canon camera instead, so i returned the Nikon (which i bought on sale) and I bought something else instead because he told me he going to give me his old better camera, but then he He said "i dont remember that, i dont think your responsible enough sorry." When he KNOWS he told me he was going to give me the camera. UGH! He always does things like that, its like he doesn't care about me at all. So i'm thinking of hiring a lawyer with my mom and making her get sole custody. Should I do that? Or what? Please help me, im desperate and my feelings are really hurt. Btw, im fifteen.