The seventh house in a horoscope pertains to one's partner. If Venus and Mars are in the 7th, the boy or the girl will have strong biological urges and so, such a person should be married to a similar one for compatibility.
Astrology can forecast a suitable marriage partner based on a detailed analysis of the horoscopes of the prospective bride and the bridegroom. According to Nadi Astrology, a lot of importance is given to Venus for males and Mars for females. The Karaka planets are Venus and Jupiter as per Vedic Astrology.
A strong lagna or ascendant (rising sign at birth) and 2nd and 7th lords can mitigate the problems of conjugal bliss to a great extent. Of course, the operating dasa (planetary period) too needs to be examined with reference and relation to the 2nd and 7th house occupier(s), lord, aspects etc.