Why is my husband being so heartless?

We had no major problems. We both work, We both pay bills, We both keep the house clean. Very good partnership. The last couple months he has been talking about life is getting routine and he's getting bored. I thought maybe he was starting to have feelings for someone at work so I asked him about it. He said I was accusing him of cheating and really got pissed. But, we worked through it and we have had our normal little fights, no big deal. My birthday was Sat. and he didn't even get me a card. He had to be at work early on Sunday, so I went out with my friend and his mother for my birthday. I came in and was loud (drunk) and woke him up and left the dogs out. This made him very angry. That's the first time I have gone out with out him in the 4 years we've been together. He goes out atleast every other week. No big deal when he wakes me up at 4 and I have to be up at 6 the only thing he ever heard from me was, did you have fun? This stupid little argument over me waking him up early turned into him telling me to get out. I packed my stuff and went to a friends house. On Monday we got together to talk and he said he wants to separate. So, I'm living out of a suit case at a friends house away from our house, our dogs and our life together because he said he needs time to figure out what he wants. He's not sure. He said he still loves me, but needs time to think. We haven't even been married 2 years. I told him he was being very selfish and taking me and his life for granted. He agreed, but says this is just how it is: I need time and space. How can he be so heartless? What should I do?