Ok, be careful here. The one thing you said that jumped right out at me is this: "The inconvenient thing is that they wouldn't actually tell me why they hated me, which actually might be the cause of this unresolved guilt."

If you don't know what you did, that doesn't mean that you have to find out what you did wrong. Guilt is all about perception (all our emotions are). What do you perceive you did wrong? This could be a certain behavior, like yelling or cheating or something. It could even be emotions, such as guilty about feeling angry or scared. It can even be about something subtle, like feeling like you pushed the person away or feeling like you screw everything up so this is just another thing.

Whatever is the target of your guilt, it comes from you, not him. It's important to then identify what you want to do about that guilt, since it needs to be resolved. Maybe the guilt is about something you really shouldn't feel guilty about, so resolving it would be about learning to accept yourself rather than condemn yourself. Or, maybe the guilt is true, in which case you can seek amends. But it's important that the amends be about you and for you. He may not accept your amends, that's ok. It's more important that you seek to amend yourself. This can sometimes be best done by seeking healthier outcomes in new relationships and allowing the guy that you used to stalk to live him new life, respecting the future that is before him as well as the new future before you.

I hope this helps somewhat, I kinda feel like it doesn't make a lot of sense.