No one deserves to be left for the mistakes he/she does or did!

no i think he should have been given a chance!

well, its not that he deserves to loose her,because if he hadn't lost lily, we would never see snape as what he is right now, loosing lily is a part of his story, if he hadn't lost her, i dont think we will know snape the way he is right now, maybe he is sad, but the thought of lily urges him to be better ..and if he hadn't lost her, then there will be no harry potter, no grumpy but loving snape, no snape fans feeling sympathetic for him..
loosing lily is just a good thing, snape needs to move on. i'd prefer snape finding another love, but bringing back the past and having her will entirely change the story.

No, he should've been given another chance at friendship and perhaps more. It's really sad. I've made a lot of mistakes in my life too and lost quite some friends because of it, which I truly hated because I probably would've stuck around instead. One of my (ex) best friends practically ignored me all year and my life was quite miserable at the time.