Your son Lagna is Sagittarius and that means he known what he wants in life. The person always looks for perfection in a relationship. Saturn which is the planet of delays and obstacles aspects Mercury, the 7th house lord. Venus the lord of gains and 6th house also aspects the 7th house, which is not good. The horoscope is weak for marital happiness. His Rahu mahadasha and Mars antardasha is going on and also the period of Shani Sade Satti. Marriage should be done after proper matching of the horoscopes.
Your son will get married in 1st half of 2018 around May-June 2018. The girl would be very disciplined and calm going. She is level-headed.
Your son might have shown interest in the last five years, which was not fruitful.