L.A.
Sounds like your son spends a lot of time with you. He had you all to himself while dad was gone and he is home schooled.
You may want to consider putting him in daycare for 3 days a week. He needs to be independent and he has not had the opportunity to do this. Once he realizes he can depend on himself during the day, he will feel better about being by himself at night.
I am assuming he will be going to kindergarten next year. There are many ways to know if your child is ready and being independent is one of them.
You all will need to all speak calmly together during the day about how getting ready for bed and then bed time will now be handled. Explain to your son that he needs to decide where a night light should be placed in his room. He needs to have a lovey to keep him safe (toy or blanket). Tell him you or your husband will read to him for 20 minutes and then he will need to go to sleep. Ask him if it would help if you were to tell him when you will be reading for the last 5 minutes so that he will know it is time for him to close his eyes.
We used to also have books on tape or CD that my daughter would listen to to help her fall asleep. She would listen to the same story every night. Once she ws older she liked falling to sleep with music and then finally a sound machine.
One of the things my mom used to do with our daughter when she spent the night away from home was to teach her how to relax her entire body. She did this by telling my daughter to close her eyes and relax her feet, my mother would lightly rub her feet, then relax her ankles, lightly rub ankles, calves.. you get the idea, all the way up top the top of her head. Eventually, my mom said once she had done this a few times, my daughter was able to relax herself, just by hearing the words, begin "relax your feet". She would just fall right to sleep.
This can be done. Just hang in there. Changes like this are best done on a friday, so that you all will have the weekend to get used to the major change.