Boyfriend has a hard time communicating with me.

He's always had a hard time communicating but not as much as it has been the past 4 months.

We've been dating for 2 years and 4 months. 4 months ago (November), he quit his corporate job and began investing everything into starting a company. During December (his depressive time) up until today, he's had little to big Trips to himself. These Trips would consist of him leaving to have time to himself. He says they are his personal time alone to cool off and not say things to hurt me. Okay, cool. I don't have a problem. My problem begins where these Trips turn into being gone for 3 or 4 hours straight without saying anything to me. Then they started occurring at night. He would leave at 11pm and not come back until 4am, or some time like that. Then they turned to overnight where he would leave at night and not come back until like 7am. These Trips then turned into going AWOL. The biggest one was for 72 hours straight. He didn't answer my texts or calls or even his dad's. I was freaking. Now for the past 3 nights he's been out and about. Going to places in the middle of the night without saying anything. I go to sleep alone and wake up alone not knowing where he went. All he can say is sorry and that he's trying. I'm trying so hard to understand him and to talk to me but he won't open up. I'm so lost and confused and feel like running. I can't take anymore of this. There are other factors that contribute to why I feel like I do.