Emotional affair 😭

My fiancé & i have been together for 4 years and last night he told me, that he likes another girl. this girl started working at his work a few weeks ago and i guess they got close and he said he has feelings for her. He told me he's not leaving me yet, he just doesn't know what to do. he wants me to give him a few weeks to decide 😭😭 what do i do?

EDIT:: I should also mention im 4 months pregnant. I have been there with him since day one, when he had nothing. i have no clue why he would need time to think.