I need advice!!!!

So my boyfriend and I have been together for 3 1/2 years. After the first month we started dating his mom kicked him out because she believed he was a drug addict. Now the thing is my boyfriend isn’t a drug addict and never was, he just smoked pot. At first we thought it was going to blow over and he would move back in but that didn’t happen. He’s been living with me and my family now since. Since he has been kicked out his mom has constantly done ridiculous things. For some examples, she called his JOB saying he was using drugs on their property and should be fired..now I don’t know about you but if I believed my child was a drug addict I don’t think I would call their job and try to get them fired. She’s also created fake Instagram accounts for us, posting our pictures writing things like “just did some crack” and followed our family, friends, and even my boyfriends managers and coworkers! She used to tell people for a year that I was pregnant & doing heroin...It has just been a never ending drama cycle! She even posted this picture on her fb last summer, and her husband made it his profile picture for 6 months!

I tried talking to her several times to come and talk with us and bury the hatchet but she always has some kind of excuse as to why she can’t come or if we did try to talk things out she would start calling ME a drug addict and blame me for the entire situation that has happened.

Now here’s where I need some advice....

So my boyfriends cousin is getting married this summer & were invited. But his cousin isn’t sure what to do because that’s my boyfriends mothers family. So my boyfriend told his cousin that he thinks his mom may start some issues at the wedding, but his cousin said he’s just going to ask her if she can keep her cool...I really am not sure what to do, I personally do not want to attend the wedding if his mother goes because it will be the first time in a few years we would be seeing her and I feel like a wedding isn’t the right place for us to talk things out. What do you all think?