Problem with friend

I have a long-distance friend and we used to talk a lot on the phone, usually in the middle of the night. Now that I have a new job, I need more rest at night, and my friend recently told me in a voice message that he needs someone to talk to right now and have long conversations with (mostly venting out his problems), and it's a pity we can't talk like we used to and it's unfortunate that I am sleeping. He said he may need to find someone else as he needs to talk to someone during the night. I always respond to his messages when I get up, but many times he is sleeping by then. He has been through very difficult times, including losing many friends and I have tried to be there for him, but I don't want to risk my health by staying up all night. I have told him I will text him when I am able and then we can talk, and will not abandon him like so many others have. He also has tried to pressure me into having sex on Skype despite the fact he has a girlfriend and more than once has shown me attitude for trivial things. If I sleep during the night instead of talking, am I abandoning him or not? I feel like I'm the bad person here

I think setting reasonable limits in order to preserve your own peace of mind is not abandonment. That being said, he may interpret it that way as it sounds like he is trying to coerce you into a relationship that you don't want to have with him.
What kind of friend is he? Why would a friend pressure you into sex (especially in view of him having a GF)? Why would a friend make unreasonable demands that undermine your own health and well-being? Why can't he talk to his GF or someone else. You can do both of you a favor by setting firm limits with him right up front.

Welcome to the forums!

You have no obligation to him. You need to sleep. He has a girlfriend and he wants to cheat on her with you....doesn't sound like a good guy. He wants you "on call" whenever he "has" to talk to you. He's using you.

You owe him nothing. Be good to yourself and end the "friendship" with this guy. He has issues. HIS issues. Not your problem. Don't get raked in. Be well.