This has happened to me before too. This probably isn’t the best advice, but I always try to pick and choose what I tell any new therapist I see in the first session, in order to let them get to know me first and for us to build rapport. For me, it worked out with my current therapist. I think it helped her conceptualize my issues easier and be more empathetic towards me. I’m not advising holding anything back or hiding anything, but it just so happened to work out for me to gradually share as trust built over time.