Long distance with newborn baby

He is 600 miles away from us and claim that his 5 and 10 year old need him.more than our 3 month old little girl. He wants to come get her for two weeks and I nurse her. We argue everyday over our baby and it's just ridiculous. He sau how his family constantly ask when are they going to see our baby. The weather is breaking and it's going to be freezing up there..why is he being so difficult about me not wanting her to go up there without me? I want to take her but only stay up for a few days. He wants to come get her and keep her without me for weeks. Saying he will just give her formula when she has been exclusively breastfed since birth. What do I do?