I sympathise with both of you, because my family is sort of a train wreck like this, and my partner doesn't really like being around them. But, you know, it's not his problem. He just doesn't spend more time with them than he needs to.

Certain people in my family just drive me nuts. Or they used to. I've gotten better at being zen about it. See, I sort of realised that expecting everybody in the world to be rational and responsible and emotionally stable is just like expecting to get all the green lights when you're driving.

Sometimes you have those days where you always get a red light, and your trip takes forever, and it makes you irrationally angry.

For some reason we as humans take simple things like this personally, even though we know intellectually that it's impossible for every aspect of our life to be easy and pleasant. Everyone has to wait at the red lights some days. Everyone has to deal with horrid people at some point in their lives. Realise that it's kind of egotistical to expect everything to run smoothly.

I try to apply that kind of thinking to the people in my family who do downright toxic or neglectful things, much like your boyfriend's mother.

You're lucky because they're not even your family, so truly, you can disengage as much as you choose.

I know it must disappoint you that you can't have a good relationship with your in-law's, but life isn't perfect. You have to shift your focus to the relationships that are easy. For instance, it's easy for me to get upset and angry that members of my immediate family are dysfunctional. But, I have a wonderful partner, in-laws, and a few siblings I get along with. You can't possibly have everything.

First step: decide you're going to disengage as much as possible.

Second step: process the anger and irritation in some way (e.g., venting on Reddit like you've done here, discussing how batshit crazy this person is with friends, telling your therapist, reading or watching docos about dysfunctional families).

Third step: find some method or mantra to help you let it go. I recommend listening to a 5-10 minute mindfulness meditation on your phone immediately before having to visit his mother (e.g. Smiling Mind app). Another trick that mind be useful is thinking of the Unwelcome Party Guest metaphor. This is designed to help with worried thoughts but can also be applied to interactions with annoying people.