Hi emillie,
I agree with waybread that you're probably in territory here where it's hard to say much that's helpful with just one aspect to go on. Posting a chart might help, if you're looking for more. If you want that level of closer scrutiny.
Entirely your decision, of course.
As I read waybread (please correct me if I'm wrong) she's saying something here that I think is helpful to keep in mind, at least as far as your NATAL Mars-Pluto aspect is concerned. All aspects have higher and lower expressions. The way to deal with a difficult aspect can't be to try and negate that aspect by neutralizing it with some other aspect.
With the millions of disagreements astro-type people can and do have, maybe the one thing we all have to agree on is that if something is in your natal, hey, that's always going to be a part of your life in one way or another. For some astrologers, in the case of hard aspects, perhaps they'd say that just leaves you up the creek. But for astrologers who advocate some notions of free will, it seems to me, the response has to be, "so with challenging aspects, better to figure out their meaning in your life and express them as positively as possible." So as I hear waybread, she's saying something I'd like to second: We have to figure out the higher expressions of our difficult NATAL aspects and live out those higher expressions, instead of the lower aspects.
From your post it sounds like you're coming out of a really difficult, trying relationship. I'm sorry to hear that.
Pointing out that we have to do our own inner work to get the best out of our own chart, and to heal, isn't intended to place blame on you for whatever happened in that relationship. I realize it can sound like that(!), but I don't think that's the intent. We weren't there. We'll never know what went on...
I get that you might actually be asking something like, "what synastry aspects should I look for in the future for a good relationship and what synastry aspects should I avoid?"
But at the same time, as the original post is actually worded, it just looks like you're asking if you can negate the pain, or possible future negative effects, of Pluto/Mars energy in your life by finding some other person with some other aspect that can neutralize Mars/Pluto effects. Again, that may not be the intent, but it reads like that. And for my two cents I just don't think things actually work that way.
Again, a clearer way to put the question might be "what kind of synastry aspects should I avoid in the future."
There to, I suspect, the answer might depend on your specific chart...