Can a creature with deathtouch be killed by a creature that it is killing?
Both creatures receive lethal damage and as a result die.

In the Comprehensive Rules it says the following regarding deathtouch:


  702.2b A creature with toughness greater than 0 that’s been dealt damage by a source with deathtouch since the last time state-based
  actions were checked is destroyed as a state-based action. See rule
  704.


So according to this rule any creature that get deathtouch damage gets destroyed.

But who gets to deal damage first? Is the the deathtouch creature? Is it because he only has to do one damage to do lethal damage? Let's find out in the next paragraph!


  510.2. Second, all combat damage that’s been assigned is dealt simultaneously. This turn-based action doesn’t use the stack. No
  player has the chance to cast spells or activate abilities between the
  time combat damage is assigned and the time it’s dealt


So the 2 damage from Gifted Atherborn and the 3 damage from a 3/3 creature is dealt simultaneously resulting in them both perishing.

If you want to destroy the enemy creature with combat damage before it kills your creature you should take a look at first strike and double strike.


  510.4. If at least one attacking or blocking creature has first strike (see rule 702.7) or double strike (see rule 702.4) as the combat
  damage step begins, the only creatures that assign combat damage in
  that step are those with first strike or double strike. After that
  step, instead of proceeding to the end of combat step, the phase gets
  a second combat damage step. The only creatures that assign combat
  damage in that step are the remaining attackers and blockers that had
  neither first strike nor double strike as the first combat damage step
  began, as well as the remaining attackers and blockers that currently
  have double strike. After that step, the phase proceeds to the end of
  combat step.