I went through similar feelings to you with T1. He would actually become defensive when I tried to talk to him about feeling abandoned and rejected and we ended up in a pattern of rupture and repair.
I left when I realised that the repeated pain I was going through was not therapeutic and any therapeutic value to the relationship was lost. I found it too hard just to leave though, so I took a 'break' for four months and consulted another (much better) therapist about my feelings toward T1 then after 4 months I realised I was making better progress with T2, so I contacted T1 to terminate.