i think there's a few different things that need to be taken into consideration here:

firstly, there are references to snape's father being a very cruel, somewhat anti-wizarding man. i think from a very early age, severus was sort of inclined to want to punish the muggle that punished him; and this is before love of a woman even entered the equation.

secondly, from an early age, severus showed a natural inclination towards the dark arts. he was fascinated by them. i think that this early fascination w/ the dark arts would've led him towards Voldemort no matter who or what he could've been redeemed by.

also, i think it's important to remember that before snape knew lily and james were in love, her friendship still didn't save him from becoming a death eater. he was already on that path, and if anything, lily was the only thing that even remotely redeemed him. that said, he still made a clear decision and understood that there would always be consequences to pay, no matter what love he did or didn't find.