Regarding telling your son, you can keep up the version of your husband being abroad for another two years at least. When the situation arises, you can say that he has gone away to a faraway place.If the child has hardly known his father, the fact of separation will not affect him emotionally. It may be a problem socially, when his friends ask him where his father is.But everything can be handled.
You should continue to give your child every opportunity to be close to your parents and spend a lot of time with them. You should also keep some hours to keep him happy: play with him, read stories to him and watch him grow.
Stop worrying about societys pressure. That is largely an imaginary monster. Divorce is not at all uncommon.