Dear readers; Is it OK for my ex boyfriend to date my sister?

From a female reader

I dated my ex to the point he asked to marry me, but when we went for genotype tests, we both tested AS. and that was where the whole relationship came to a stop. We tried to wave it aside, but it was not possible, considering the future.  We never had sex while in the relationship but we kissed and we felt strongly for each other.

We have moved on, or would I say, I have moved on, cos am dating now, but he is not dating yet. My ex is so nice and am asking him to start a relationship with my sister and see if it will go far, since we didn't have sex. Please I would wanna seek Libers opinion on this. Is it weird?