Take a deep breath and relax. Everyone who has Mars in the 8th is NOT going to die young or have some kind of accident. That would be millions of people and that's obviously unrealistic. Furthermore, there have been millions of people who have died young or had an accident that do NOT have Mars in the 8th house. So things are as simple as you think. One placement cannot doom you, that would be ludicrous.
As for whole sign versus other house systems, that's a personal choice. Most of us in the West (US & Canada, Europe, Australia, etc.) use the Placidus system rather than whole sign. Whole signs are typically more common in Vedic (Indian) astrology and throughout other parts of the East. Look at your chart using both systems and compare. See which one describes you better and feels more "right."
As for finding love again, that's a question that might be good for a horary chart (Google for a good explanation on what those are if you don't already know, I'm terrible at explaining things sometimes!). It basically helps you predict the outcome of matters. You look at the exact time when you first think of a question you really want the answer to -- something meaningful to you and not something silly like "Will I have desert later?" Then you make a chart for the question using the exact date and time you thought of the question (same process as you would for drawing up a natal chart). You can only ask once unless matters change.
For instance, I can only ask a question once every three or 6 months or so (giving the situation time to develop and change) unless things change before then. For instance, if I want to know will I get hired for a certain job and my question was "Will I marry my boyfriend?" I can only ask that once in a, let's say, 5 month period (and if I ask again it has to be because something happened to make me think that the original horary chart's answer may have changed and I really want to know -- for instance, if I asked 5 months ago because I was hoping he would propose and the chart said "no," but 5 months later he brought up the topic of marriage for the first time or expressed he likes the idea of it, so I reask to see if maybe he has changed his mind). Mind you, you can't ask things that are going to be too far in the future. For instance, a 10 year old can't ask "when will I get married?" and expect the chart to be valid. She might ask "Will Bobby take me to the dance next Spring?" and get a valid response. It works for about up to a year or so.
Now, if in 3 weeks or 5 days, or whenever, the situation changes in a way that makes you question the original chart's validity, then you can reask and see if the situation or outcome might change. So next time you are feeling like you REALLY need to know if you will find love, note the time and make the chart and post it on here for interpretation.
You can post your natal chart and someone on the forum might be able to help you make sense of things, but predictive matters tend to be better with horary. Transists might help too, but I don't know how specific they are. In any case, relationships tend to be difficult for most people (finding someone, falling in love, staying stable, etc.) so you aren't alone. I'm sure you're not doomed!
