If it’s not mortal, it’s venial.
Then it wouldn’t be such a serious issue, would it?
http://www.vatican.va/archive/ccc_css/archive/catechism/index/d.htm
About 3/4 the way down is all the references in the CCC on divorce with links to take you to the statements.
Those in the process of divorce cannot take communion unless certain conditions are met.
So, tell me again how divorce is not a mortal sin?
It sure seems serious enough to have the church take a stand against Catholics divorcing taking communion, that is until they get an official annulment from the church.
A more convoluted system of religiosity does not exist. Catholics can find ways to finesse God’s directives in ways that would make the Pharisees blush with shame that they hadn’t thought of it.
Since you have shown that you have an incomplete knowledge of both the spirit and the letter of canon law, why not drop it?