I don't think your T will think any less of you.
The situation that just happened does take anything away from what you've already accomplished, how strong you've been and how well you've set limits.
Your T sounds reasonable and understanding, and therefore would not expect you to be perfect. The way he described your ex, as a chronically draining person, also indicates that he will be understanding of the situation.
Take good care of yourself, ((((((((((((Mixed Up))))))))))))))))