As a current LARPer and MUer, I'm not super prone to bleed these days. I'm not sure why that is because I was certainly way more vulnerable to it when I was younger and experienced a certain amount of it. I was fortunate that it never had destructive consequences and that the people I larped and mu*ed around were constructive, healthy enough to participate in making sure there were boundaries to prevent that.
When I was in mid-20s, I was in a game where my PC was in an intense romantic relationship with another PC. The game was online but myself and the other player knew each other from local larp circles, so we were friends offline before this pairing in-game happened. He happened to be married at the time. I was not. Things sloshed over for both of us in terms of bleed. We were able to hit the breaks, acknowledge there were feelings that while 'real' they probably didn't actually mean that we wanted to hit self-destruct on our social circle and his marriage just because we felt that way, this was an infatuation, and we just let the thing run its course.
I was lucky because if we hadn't taken a step back, we probably would have enthusiastically let bleed dictate behavior, a huge explosion would have happened, and at the end of all that, it would be the last few minutes of The Graduate but in real life, so the slow seep of regret and divorce attorneys.
This is all to say that I think the first step is acknowledging that it happens and that none of us are robots and that brains and hearts are easily mutable and changeable things when it comes to manufacturing emotions and then leaving them unattended. And I think having serious conversations with the people around you that you trust about how to pull the fire alarm if something happens, before it happens.
And there are other kinds of bleed for sure. Nordic format larps and some MU* are really good at the suffer puppet game where intensely shitty stuff happens in a game and then you're stuck in your feelings about it. The larps at least have a de-role and debrief process that gives you tools to separate yourself from the events at the very end of the event (often with mental health professionals involved)-
A de-role exercise I really like is taking a piece of your PCs costume and then literally putting it in a box and basically giving your PC a eulogy. It really helps, I think, with reframing context: this PC was 'alive' for a weekend and now, it's not. There was then and this is now.
I think some of these exercises can be translated into MU* spaces.