The feeling is uneven. It lasts if you keep adjusting, not if you wait to match.
The two of you
Gemini. You feel real when the conversation is alive. People see the quick mind, and someone who can talk to anyone.
Capricorn. You feel real when you have carried it and it held. People see the backbone. They give you the responsibility.
What wears it out
Being told to pick one thing and stay there drains you. Silence that means you should stop asking does too.
Being the only adult drains you. Rest can feel like failure even when you need it.
Gemini needs to talk before it feels real and adapts quickly, and may not finish. Capricorn wants something solid and starts things.
Nothing in the two signs locks on its own. Some days you understand each other. Some days you are solving different problems in the same room. Together, it shows up as sex and what they cannot take lightly. The other way around, it shows up as the work of an ordinary day.
This is the answer people want before anyone knows a birth time. Two real people have more than a sun sign. If it matters, cast both charts.