I think you are just getting caught in a mental trap. Who he is seeing, who he isn't, why he isn't calling you, why he doesn't want to, and so on. What's the difference? No matter the reason, the result is the same. You are looking for answers only he will provide and he isn't going to tell you them. It's fruitless. If he was dating another girl and talking to you that would be pretty messed up anyway.
Look at his actions. He isn't talking to you. Isn't that enough? You have your own life to be concerned with. I know you probably have a tough workload and it's killing your fun time, but when you do have some free time, you should do stuff. There is alot out there.
Waking up next to a beautiful girl,
Step outside and say hello to my beautiful world.