Help needed with relationship advice please

I have recently been in a relationship with my partner for 7months. He's the most caring ever ! He did used to joke about ocd and being autistic but as the months went on I noticed some trates ( I work in a special needs school ) we have done the test and he clearly is autistic BUT what I am struggling with is our relationship. He seems to think I lie about things which then spiral into senarios in his head. He can be awful and say mean things and does not listen to an explanation or how I feel. He can completely block me out of his life which makes me feel like he doesn't care. Has anyone else experienced this ? Constantly being accused of lying and then he can repeat the same argument days maybe a week later as it will come back into his head. I love him dearly he's amazing and so funny but this has ruined us both . He can't accept I have been faithful or My way of thinking is acceptable