Izzy's "Third Wheel Friend" is about feeling tolerated rather than wanted. The speaker sees friends who seem warm on the surface, who talk to her and act as if she matters, but she is convinced they escape whenever they can. In her view, they stay only to avoid her being upset and to spare themselves guilt. The image of dogs on leashes makes this vivid: she imagines herself as the thing holding them back, a restraint they would slip if they could.
The tone is quiet, hurt, and resigned. The speaker doesn't shout or accuse; she seems to accept the situation as "easy to understand." She feels she has too much to live up to and cannot keep pace, so she lags behind, waiting for a happiness she believes will never arrive. The final line, "Because I am the third wheel friend," lands like a verdict she has already passed on herself. What lingers is loneliness, and the sense that her self-doubt may be shaping how she reads her friends.