You can say “God forbid. Is it not just sex?”. But to be honest, “just sex” does not end with a side chic taking over your business, in fact it is only the beginning. You may still be living with your husband, but your marriage has lost everything that made it what it was.
I don’t know what this pregnancy is costing you, but love lives have been drained, homes broken and many have fallen into depression, most of which can be traced to unsatisfying sex in pregnancy.