B.H.
It's totally normal for the kids to have seperation anxiety and not want mom to leave or be left alone at school. I would totally put him in preschool and get him used to it now. So by the time kindergarten comes he won't be freaked out. I had my daughter in preschool at ages 3 and 4. She never cried thankfully and when kindergarten came along she did awesome no tears, nothing. I know there were a few other kids in kindergarten that cried daily for weeks. So I would try and get him used to the idea as much as possible.
Sometimes us parents have to have tough love, it's hard but it makes our children better and in the long run everyone is happy.