I've had a slightly similar situation and when T showed up at a function I was helping run, I hid and had a friend tell me what she was doing :-)

If his child is part-time and you are not directly in contact (in his class, for example) with the child, then I would not worry about possible contact until it happens. People run into their T's all the time in regular life, at stores, for example. I remember my girlfriend was a teacher and her students would run into her (similar situation as they are teens/children) and I ran into one of my high school teachers when I was in college, he was taking some courses there too! That was awkward

It may be awkward but probably won't affect your therapy. Once the interaction is over and you are "safe" again :-) it will actually be kind of nice, like T was actually in your actual life and a "real" person.