The best way to stay motivated when running on your own is to look at the bright side! If you are going from running with friends who keep you accountable and provide good company and conversation, start by considering all the benefits of running on your own without others.
First off, the alone time. Especially since you are running in the early mornings before work, this is a great opportunity or you to think and plan for your busy day ahead. Running is also a great way for you to clear your head, which can be especially necessary if you are really bogged down with work, priorities, and anxiety.
Second, make it easy on yourself to get out the door. Limit the excuses you could find that might deter you. Go to bed at a decent hour so that it's easier to get up in the morning. Lay out your clothes and running gear the night before so you can quickly get ready (which includes checking the weather and running conditions so you can plan accordingly). Plan your routes ahead of time so you know exactly where you're running.
Also, think about how much BETTER you feel after a run! Oftentimes, our entire day goes better and feels more ordered when we start off by getting our heart pumping, clearing our minds, and doing something good for ourselves. It can really set the pace to have a great, productive day. And if you're worried about accountability, ask your running friends if they wouldn't mind you texting or calling them to talk about your running, running in general, etc. This way, you still have that accountability from afar - after all, you have to actually go for a run in order to be able to tell your friends about it!
Music helps too. Especially on those mornings when you're only confined to a treadmill. If you're not a morning person, it might help to give yourself some kind of incentive. For example, give yourself some spare time to treat yourself to your favorite coffee or breakfast afterward.