Venus is the Karaka or significator for all things that deal with luxuries, comforts, enjoyments and pleasure. So he also deals with the conjugal relationships and the pleasure of having company of others.

In the Rasi chart The 7th house deals with how you view and deal with the world or how the world is coming to you. The planets in the 7th indicate your attitude towards relationships as well. For example Lord Sri Rama was a very gentle, wise and peace loving person ( Asc with Jup and Moon in a Sattwic Cancer ), but had exalted Mars in the 7th - his world was always about conflict, being a warrior, fighting demons, fighting or being in battles etc.,Planets in the 7th house indicate what kind of people you are looking for or more likely to hope for (not explicitly but also instinctively)

Arudha of the 7th house A7 (planets in conjunction with A7, aspecting A7 or lord of A7 if no planets influenceing) indicates what kind of people one associates - Mercury - intellectual, Jupiter - wise and learned, Moon - highly social people, Sun - political etc.,

In general a marriage between a two consenting individuals is all about sacrifice and sharing. The couple have to share their living space, spend their incomes on the other, investing time, money, effort for family/children/or even in-laws. Since marriage does involve giving, losing, sharing or sacrificing - the Arudha of the 12th often called as Upapada lagna is of high importance in wedding/marital analysis.

Upapada Lagna - This is the Arudha of the 12th house in the Rasi chart. Take the lord of the 12th house and count the distance from house to lord. Count the same distance from the lord. If this place is in 1st or 7th from 12th house then count ten more house. This is how we calculate the Upapada lagna. The calculation is just like Arudha lagna - but here we use the 12th house as a basis.For example : Cancer Ascendant; 12L Mercury is in Leo (3 house away from 12th) - then count 3 from Leo - places the Upapada lagna in Libra. (No exception need to be applied)Leo Ascendant; 12L Moon is in Libra (4 houses away from 12th) - then count 4 from Libra - this place (Capricorn) is in the 7th from 12th (Cancer) - so countten more houses - the UL is placed in Libra again.

The planets in the Upapada Lagna or planets aspecting the UL provide some indications about the partner his nature, attitudes, tendencies - some clues about his profession etc., The placement of the UL lord give some indications about his position in the society - whether rich or middle class;Too many malefics influencing the UL without any benefics can cause serious delays or denial of marriage - when there are mixed influences the wedding may happen, but the marriage will have anger, frustration, conflict (Mars), sorrow, pain and suffering (Saturn) and shock and lies (Rahu), too much conservative, religious views (Ketu) etc.,

2nd from UL indicates the sustenance of the marriage - Malefics influences on the UL, but benefics in 2nd from UL indicate painful wedding but the pain will continue by sustained marriage. Benefics in UL but malefics in 2nd from UL - good marriage but circumstances will cause the break or end of marriage.

3rd and the 8th from the UL indicate the strength, length and vitality of this wedding/marriage. 2nd and 7th indicates weakness (marakas) to the UL. 9th indicates

the blessings in this marriage and the 11th from UL indicate the gains out of this marriage.Planets in the 7th also indicates opposition forces to this marriage.

In the olden days the world of relationships, marriage, weddings were very simplistic and straightforward - nowadays this have evolved so much there is so many variations to relationships - including concepts of dating, living together, extramarital affairs, illicit relations etc.,

A relationship that last less than 1 yr is mostly considered to be a temporary one and should be mostly seen from the A7, Permanent ones are mostly to be seen from the UL.

When one marriage ends the next marriage (or the potential for the next) is seen from the 8th from the UL. The next one begins where the first ends. As one can see if there are multiple malefics influencing the 2nd from UL1 (UL1 now indicates first marriage) - there is a strong possibility that these malefics are now in the 7th from the UL2 - this we find that 2nd marriages are not so easy to come by - take very long time and labored For example if UL1 is in Aquarius and Pisces has Mars and Saturn causing break up of UL1; UL2 seen from Virgo has Mars and Saturn in the 7th from UL2.

Moving on to NavamsaThe Navamsa gives the scenario at home after the wedding is all done - the environment of home in the marital life.7th in the Navamsa indicates the how the first marriage is going to be; benefics good, malefics bad.Mars in the 7th - fights, arguments, conflicts, anger, aggression.Saturn in the 7th - sadness, pain and suffering, coldness.Rahu opposing views, may be from other cultures, backgrounds - not just intercaste - just a general difference of opinion.Ketu too religious or dogmatic also opposing views.Sun - authoritative, independent, egoistic, prideMercury - intellectual, talkative, Jupiter and Venus - ideal, supportive, romantic (Venus)Moon - social, many friends, compassionate.

2nd from the 7th also indicate what will cause the first marriage to be sustained or breakup - benefics good, malefics bad.Again following same principles as UL1 - but the 7th is the what kind of partner you actually get - not the 7th you were hoping to get (that is seen from 7th in Rasi)

In Navamsa the 6th house can indicate fights, obstacles, own weaknesses etc., and 8th indicate the sustenance to the first marriage.So involvement of the 7th lord in 6H is usually not very auspicious. Also 6L involved in 8H and 8L involved in 7th is highly detrimental to marital bliss. Also look for Arudhas of 6th and 8th and planets in these Arudhas are most often involved in triggering problems and causing damage.7th lord in 8th is usually considered very good and auspicious unless afflicted. 

Again for subsequent marriages - analyze the 8th to the 7th and so on.

The 6th house indicate growth or expansion; So I would opine that 6th from 7th would indicate some sort of addition - in terms of relation may also indicate other interests (not

necessarily extra marital or illicit). If we review carefully 6th from 7th is usually the 12th from the Ascendant and can indicate the native going away or foreign places for some reason or other - can indicate foreign for business or living abroad or may need to be separated due to some other duties/responsibilities.

I've also noted that involvement of the 7L in the 2nd has mostly caused the native to gain from his/her spouse - the native's asset increases after marriage or the spouse itself is very supportive and is indeed an resource/asset to the Native