No worries your basil is safe to eat as long as you make sure no poisonous leaves or plant parts have fallen into the harvest so that you accidently eat them. The Basil will not absorb poison from the roots of the Oleander.  Basil loves sun and heat so your plants will do better and you will rest easier if you don't grow basil beneath any plant. The wild pulsane is also a plant you want to weed and keep away from the basil so it does not rob the soil or nutrients or water that should go to your basil. It is not too late to dig up and move your Basil to a more isolated location. Or grow it in a container on your patio where it will be close by for summer salads and safe pesto. Keep growing, Marianne Binetti