living separate to 'save' money

My BF just informed me that he thinks it might be a better idea for us to start living separately again. We have been living together for about 1 1/2- 2 years now and we have our third child on the way. Our relationship hasn't been the best but it hasn't been the worst either, but I feel like this is his way of saying he wants to break up. He has been acting strangely for the past couple of weeks and I always joke around and say he is talking to other women, but I have never actually believed that. Now, I'm not to sure what to believe. I just feel so crushed. Like, out of all our ups and downs, this is not something I expected. And I'm literally crushed about it.