I am Mars exalted in Capricorn combust Sun in the 10th house which gives me power.
You're being stripped of power, meaning you're powerless. The light of the Sun is drowning you out so you can't even be seen.
I am in his turned 4th house.
You're getting way ahead of yourself there.
The biggest mistake I see people making is that they have no system, so they jump around haphazardly and miss 90% of the stuff then come to all the wrong conclusions because they do.
You need to develop your own system, one that's both logical and comfortable to you, and write your judgments out, because it reinforces your system.
I always look to see if the chart is valid. There's no point wasting time on an invalid chart. This is chart is valid because Mercury is the Hour Ruler and is in the same Triplicity as the Ascendant.
You need tables to calculate the Hour Ruler (unless your software does) and you can find those on the internet. Lily explains it. So does Gadbury. There are independent tables as well.
After that, look at the strictures and warnings: Asc or Moon Via Combusta, Moon Void of Course,
and Saturn in the 1st or 7th House when not a primary significator (strictures and warnings
never render a chart invalid -- they only warn the astrologer that there are special or unusual circumstances that affect the Querent and need to be taken into consideration -- so they're sometimes called "considerations" too).
Saturn is sitting right there in the 7th House. That is a warning to the astrologer that the astrologer does not have enough information to judge the chart accurately. The reasons why the astrologer doesn't have enough information are too many to list here.
Having determined the validity of the chart, and then looked for warnings, I assign significators, determine their strengths/weaknesses and then start judging each one individually. That's how I do it, but you all can do it any way you want, so long as you do it consistently.
the significator of the Querent Combust, shows him or her in great fear, and over powered by some great person.
and you must know that the combustion of any Planet is the greatest misfortune that can be.
Mars does receive Sun by Exaltation, but Mars and Sun are Planetary Enemies so this can never be something positive (unless Mars is Cazimi).
He is Venus in Sag in the eighth house feeling unfortunate.
That would not be the correct signification, and even if it would be, that is your 8th House, not his. That's his 2nd House.
Saturn in Libra has made an earlier square to Mars (me) not sure if Saturn is her in his 7th or not.
Ah, now we come to the Saturn in the 7th, Mars Combust thing. This questions is probably "Is he cheating on me?" or something similar.
The 7th Consideration, is to beware of those cases wherein the Astrologer is subject to err and mistake; of which the learned have named four: 1st When the Querent is so silly that he knows not how to ask, nor what he would have....
You have to know
exactly what it is you want to know, and you must be absolutely specific about it.
If the question really is
"Is he cheating on me?" then your delineation is wrong because we use a totally different method of delineation for that question. If in the alternative your question really is,
"Will he take me back/Will we be together again?" then your delineation method is incorrect because we have totally completely different method of judging that question as well.
Both of those questions are advanced Horary, because they require knowing how to use Triplicity Rulers.