I don't think the answers above are correct. Infidelity during a relationship which has not been disclosed can be seen as "misrepresentation" and will lead to being found inadmissible.
see: https://www.canlii.org/en/ca/fct/doc/2015/2015fc769/2015fc769.html?searchUrlHash=AAAAAQAdcGVybWFuZW50IHJlc2lkZW50IGluZmlkZWxpdHkAAAAAAQ&resultIndex=34
There are lots of cases like this on Canlii
see: https://www.canlii.org/en/ca/fct/doc/2015/2015fc769/2015fc769.html?searchUrlHash=AAAAAQAdcGVybWFuZW50IHJlc2lkZW50IGluZmlkZWxpdHkAAAAAAQ&resultIndex=34
There are lots of cases like this on Canlii