Sorry you went through such an upsetting situation. It sounds like you were splitting on L, and I understand that must have been really painful. I don't experience splitting myself, but there are certain areas that are very sensitive for me and I am at risk for cognitive distortions and emotional dysregulation when those buttons are pushed. Even when something is a cognitive distortion, I realize that it feels real and the resulting distress is real - so I'm definitely not trying to minimize your feelings when I talk about cognitive distortions and dysregulation. What I personally find helpful is to identify the belief(s) that an event has triggered then look at the evidence for and against that belief. For example, I sometimes start thinking the therapist doesn't care about me. It helps to remind myself of all the things she has done that are inconsistent with that belief.

I realize it sounds a bit like I'm suggesting some sort of CBT thing (I actually don't have a very positive opinion of CBT), but I haven't actually received CBT and this method is just something I started doing naturally to soothe myself. I think DBT might have a skill called "checking the facts" that may be similar, but not 100% on that. Anyway, this strategy helps me slow down Mr. Toad's Wild Ride (aka my emotional reaction). The idea is not to discount the emotions, but to check the beliefs for flaws and weaknesses. Sometimes a belief is justified - it's important not to enter the analysis with the intention of gaslighting yourself. But lots of times (for me, at least), there are factors warranting consideration that are easily overlooked in the heat of the moment.