Partner's personality changes

I'm a long time lurker and I finally mustered up the courage to post. My partner was diagnosed with stage 3 glioblastoma a few years ago. Tumor was removed from the parietal lobe and resected. He's already done the radiation and chemo. But his personality has really changed these past several months. He's gotten more aggressive and combative with me and gets upset very easily. A year ago, we were so happy and things were great. I love him very much and have tried to make things work out. He's told me he wants things to work out, but cannot make any guarantees. He says he loves me, but is no longer in love with me. I was very hurt by this and I even asked him what I did wrong. He says I've done nothing wrong. He says its him and doesn't know how to be a good boyfriend. He moved out and I told him I still love him and I hope we can work our way back to each other. I'm having a very hard time dealing with this and my heart is breaking. I'm hoping there is someone out there who can relate or has (or is) going through something similar.