Christina offered some amazing suggestions. I think physical validation of your thoughts is an excellent way to prove something real or unreal.

Assuming you are dealing with thoughts that aren't physically proven I think it would still be a good idea to write them down. Make a list of the proof you have to support each claim as well as the proof you have to deny it.

Example:
'H doesn't want me around'.
Evidence this is true - my thoughts tell me this is true. I think he is lying

Evidence this is false - H comes home to me every day even though he could freely go. H tells me he wants to be with me. H spends time with me when he could be alone. H cares about my therapy and wellbeing. H takes me places with him when he leaves instead of leaving me alone. Etc.

I think in most cases it will be clear your supporting evidence comes from your thoughts and you already know those are corrupted. You will see the evidence against your thoughts is based on real actions of people. True, it is possible people could be lying to you, but in the case above you have years of repeated action as evidence to deny your thoughts as well. Logically the thoughts fail the burden of proof test.