How are you doing? You have a scorpio navamsha rising when you say Aries is 6th house and Gemini is 8th house in navamsha. Mars-Venus combination in 8th house in Gemini navamsha could indicate troubles or breakups in marriage due to hidden romantic affairs. Now this doesn't mean it will happen. Events of your life will be decided by the mahadsha time period you are running, not by any combination in chart.
Navamsa says about spouse from lagna to 12th everything says about spouse .
if you say ketu in 6th aries means he is scorpio asc . for scorpio ketu is co ruler of lagna so he has all the qulaities of mars as lagnathipathi as well as 6th house matters . he is robust , sound health , broad shoulders , short temper , slender physique . masuline body (assuming jupiter is not influencing lagna )
ketu in 6th is very good over all success no enemies , no debts etc etc . person has superiority complex since he has high level of courage . has weird apetite . his maternal uncle suffers . aries rules head so he may have head realed issues he acts without thinking . he will go first if fight happens anywhere . angry person . hot blood but all these depends much on mars , above said will come full if mars is placed well else reverse happens .
venus mars combination makes the person playboy . upto the level of spoiling their health . it also goes under the name kuja dosh . creates problems in married life , this combination is only good for sex life and not for marriage . relationship with sisters and aunt will also suffers .
if this combination occured in kendra or kona its nice but not in 8th house
forgot to mention . for scorp asc mars 6th lord in 8th goes in the name called vibreetha raja yoga sudden change in life after marriage . everything is nice except married life both of the partners indulges in sexual adventures , it will not happen if jupiter aspects 8th house ...