OP, you describe your self as working full-time, cleaning the house , and doing a majority of the childcare. Those are all admirable traits, but they are not the traits that cause people to fall in love. If that were the case, people would fall in love with their housekeepers, and nannys.
Relationships have to be nurtured, and it does not sound as though either of you spent much time nurturing the personal relationship between the 2 of you.
Instead he looked elsewhere, and you confused domestic activities as an adequate substitute for working on the relationship between the 2 of you.
It may be too late to salvage your marriage, but it is not too late to become reacquainted with yourself as person who is not only an employee, housekeeper, and a personally invested childcare provider, but also a person with interests, opinions, goals, hobbies, and passions. That person has probably not shown up in your marriage for quite a while. The time demands of working, cleaning, and parenting are exhausting but letting this solely define you comes at a cost.
I am not excusing or justifying your husband' s cheating behavior, because an honorable man would have left and then pursued his next relationship. But when you say that you loved him, you probably were just content with the familiar and not at all acquainted with his evolving interests, goals, hobbies, and passions. The pain now probably comes from the loss of the familiar (not necessarily the loss of this particular man whom you may no longer know ) and the fear of the unknown.
However, this particular situation evolves, use this time to become reacquainted with yourself. You are a strong person , and you can manage all of the tasks ahead of you without sacrificing or submerging the various parts of your identity and personality.