My fiancé went off his meds and destroyed our relationship. I'm struggling to cope with the guilt I feel for trying to move on.

Basically what the title says, my fiancé (diagnosed schizophrenic but possibly schizoaffective?) went off his meds and turned into a different person. (At the time he was adamant he was still taking them and acted offended that i even suggested he wasn't)

He rather coldly broke up with me several months ago and quickly jumped into a new relationship with a girl 9 years younger. It completely shattered me. I was devastated to the point I went to church (atheist) just trying to find some reason to keep going. Eventually I made some friends and met a nice person that was interested in me although I kept a bit of distance. However, around the time I was finally starting to move on my ex-fiancé explains he went off his meds and how everything was a huge mistake and he never really wanted any of it to happen. He says he can't live without me and that I'm "his light." This has shattered me even more because I've always felt immense responsibility in keeping trying to keep him upright. I still love and care for him deeply but I genuinely fear being with him again after the pain I went through. I'm scared he's going to hurt himself or worse. I also have no idea to what level I can trust and believe him or even believe he ever went off his meds at all and it's not just an excuse. There were many lies during our relationships so I don't know what to believe anymore.

I don't know what sort of advice i'm looking for but if anyone has similar experiences and can maybe share what they've been through that would be nice. Thank you