Ymir and Historia got married, they had been living alone for 4 years, everything continued like this until Historia convinced Ymir to adopt a child. They went to the orphanage and saw you there

Historia: look! I think I found the one!

she said pointing at you excitedly while looking at Ymir

Ymir: yes I think it's a good option

she said without even paying attention to you, she just wanted to make her beloved Historia happy