I feel the same way about my T. She has said she cares about me very much, but I, like you, don't trust it will last and I need to hear it all the time. As I didn't get that from my parents either, I'm looking to fill that hole. And I agree with 2or3things, that we have to give it to ourselves.
That is the hardest, sucky-est thing to do. Now, on top of wanting to hear she cares about me often, I'm also jealous of others in her life and am having to deal with that stuff.
I would say that it could be helpful to keep this line of communication open with her, as it will bring up other stuff for you to work on. Because, as my T says, it's always about something else and it's always about me.
I now believe she could say it everyday and I'd still be questioning it. We've been working on how this relates to my childhood and what I never got that was healthy and what I always got that was unhealthy.
I guess what I'm saying is to stick with the feeling and use it to work on the stuff it brings up for you. I know it's hard and all you want to hear is, "I love you", but be prepared to not hear it and get that love from yourself. Because we didn't get it from the persons who we should have gotten it from....just like 2or3things said.
Good thoughts to you!!