My cofounder keeps making decisions without me. What do I do?

This is a governance failure, not a communication problem. Talking about feelings will not fix an undefined power structure.

Decisions flow around you because decision rights were never defined. Where no structure exists, the faster mover becomes the de facto CEO — and that has already happened.

This week, set a written decision matrix: which calls require both signatures, which are solo. If your cofounder refuses to put it in writing, that refusal is your real answer.