i don't have many cavalary because i lose equites very quickly
Equites are light cavalry, not a shock unit like Cataphracts, and as such should never be used in frontal assaults unless it's a dire emergency. They should not engage spear units at all, even from the rear, unless you have already forced the phalanx unit to its' secondary weapon (usually a sword). Equites should be out covering your flanks, or circling behind enemy lines to get at missile units.

In a Brutii campaign, the biggest threat to Equite, outside of spears, are Macedonian Light Lancers. Lancers are mounted spear that get a hefty charge bonus that often will crush your Equite. The secret is to engage them before they can bring home a charge, thereby negating any bonus. Without that charge bonus, Equite will eat them up because they have better melee stats.

Greek Cavalry and Equite are about evenly matched, so you need superior tactics (or a better general) to win. When you get Cavalry Auxillia, you can bait them into chasing the Auxillia (which are faster), and flank with Equite.