It is not the feelings of jealousy that are the problem, as this is a common response in new fathers. But it is the fact of his withdrawal from the family, based upon these feelings that could communicate a destructive message to his son. It is not your job to dole out nurturance. And you need nurturing, too. For therein lies the connection he longs for.
Sex is a transient and empty substitute for enduring intimacy.
It is common for men who have experienced difficulty attaching to their own mothers as infants, to seek connection through sex. However sexual connection alone never satiates the deep need for intimacy and contact that is an important part of finding your place in a family. Your commitment and devotion to him should give him cause to consider looking inside for some of the answer to his own need to feel included in your love. And if the two of you are both working full time and parenting, it is true that your attention to one another is curtailed. Going to school in addition could also be leaving little time for each other or parenting.