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I am sorry to hear about this situation. If you stop making payments, and the other party stops making payments, and the lender reports the missed payments to credit agencies, then your score will suffer. How much depends on a manu nuanced factors of a formula that is not public, but you can go to www.creditkarma.com, log in, and do a "what if" scenario to see how your credit would be affected (note that the scores there are what are known as "FAKO" scores, but they are basically 2-5 points off your actual score).
I am sorry to say that there is nothing that can proactively be done aside continuing to pay the loan. One can ask that they not report this on one's credit, but it is the lender's decision.
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