A new stepparent doesn’t need your love on day one. Respect is a fair starting point for both of you.

Love is not something anybody can produce on request, and treating it as the expectation puts two people in an impossible spot on the first day. Respect is available immediately and does not require pretending. It means ordinary civility in both directions, with no performance of a closeness that is not there yet. Whatever comes later can come later, or not.

Aim for being decent rather than warm for now. Say hello, answer questions, keep the sarcasm down at dinner. You are allowed to expect the same back, and if you are not getting it, tell your own parent plainly rather than absorbing it.