It didn't happen with my T but it happened with my "big sister" at church. A relationship that spanned over a decade. We were so close I spent holidays at her house etc and we talked every day.
In retrospect there were personality issues I should have been aware of in the beginning. But I was desperate to be loved. And for a very long time she loved me more than anyone in my life ever had. She was literally my family to me since I an estranged from.my abusive FOM.
Then I got sick. I was hospitalized multiple times. They couldn't figure out what was wrong with me. I was in excruciating pain and saw specialist after specialist. I had iv treatments in hospital monthly but they couldn't figure it out. I was losing weight, getting weak, lost my period, excruciating muscle pain constantly....
In retrospect now with almost a decade behind me I can admit that I got very clingy and needy and a bit unreasonable. Though I also think.under the same circumstances a lot of people would. I finally got a diagnosis. The disease was not treatable and would change my entire life forever.
She decided she was sick of me. Refused to visit me in the hospital and then sent me an email saying she never wanted to see me again. And she meant it. I saw her husband once to get some of my clothes, books. Dishes etc that had been borrowed back but she never spoke to Me again.

It was utterly devastating. I considered suicide on and off for a year. I cried constantly. I lost interest in my life.

Only two things really helped. The first was time. It still hurts but after 9 years the pain is less fresh.
The other was realizing they she had her own deep seated issues and was acting out of them and it didn't say anything about who I was. That freed me up to trust again though I doubt I'll ever trust anyone the way I trusted my big sister.

It was a devastating journey. But I'm in one piece on the other side. The best thing was to.keep telling myself for the first year or two that it wouldn't always hurt so badly, that sooner or later the pain would finally start to ebb.

I wish you peace in your journey.