All the positive momentum is on your side. YOU taking some form of control over you own life by both uncovering the truth and making her and your cousin face at least some level of consequences for their actions. Nothing has changed on her side that I can see except that she isn't getting away with it anymore. Her feelings haven't changed. The way she treats you hasn't changed. Hopefully it will, but there isn't anything you can do to make that happen.
I honestly have no idea what to recommend to you from here. I approached my marriage from a VERY different perspective- and cultural background. I had no desire to make a life with someone who wasn't in love with me and ready to do whatever he could to heal me and our marriage. I asked my husband to search his soul and decide what he really wanted. If he didn't want 100% to be with me - I WANTED him to leave. Simple as that. I had no desire to "convince" him to love me. I had no desire to compete in any way for his attention. I had no desire to monitor his actions. In fact, I thought then (and still do now) that he was INCREDIBLY lucky that I was even willing to give him a second chance. So if he wasn't ready to grab that chance with both hands - then he needed to leave so I could grieve our relationship and then move on to a relationship worthy of me. So as you can probably imagine it is very hard for me to understand, or provide any assistance in your situation. Because my honest reaction is "send her packing" if she isn't ready to fight for YOU and your marriage. I am not saying you are wrong for your approach - I have no idea if one approach is better than the other. I am only saying that our very, very different perspectives makes it difficult for me to provide any helpful or actionable advice.
BS - Female
Married 27 years, one adult child DD May 2016 “When we are no longer able to change a situation, we are challenged to change ourselves.” - V Frankl