seninle oldugu sanýlýyordu

 he? she was imagining it/she /he was with you

my try but not sure

My attempt (but not sure, wait for clevers):

He/she was regarded (considered) to be with you.

 You are one of the clevers!

This is correct. It might be more natural in English to turn it from passive to active: We thought he/she was with you, or we thought you two were together. But yours is literal and right!

Thank you very much Marion I thought about translating it the way you did, but I wasn´t sure and decided to do it literally.