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Maybe he wants freedom.

As long as he doesn't end up as dog stew, all should be well.

I'm no dog expert let me start with that but did your dog spend most of his days inside or in a confined outside space/yard?
If so then he was excited to run off because open space. And if he can find his needs straying around he's not going to pay you any mind.
Him howling or barking could mean A) Heat. He needs to F***. or B) He was lamenting too if your recently passed dog lived with him. Dogs make connections too. That dog was a part of his pack and if that dog died and suddenly disappeared that can cause distress. So being around those stray dogs is him coping and moving on.

You said you never were harsh or mean to the dog, and I'm not making accusations just food for thought, did your family members ever get aggressive or mean towards him? I mean they did demand you "kick him out" due to howling. An owner can do all the right things but if someone living with them does the opposite it send mixed singles to the animal and with dogs that can be detrimental. They need stability when it comes to human interaction. Even a well trained service dog doesn't like to be yelled at or treated poorly.

And my last point is, did you ever train him completely? You say he would run around nonstop and ignore commands. Maybe the connection you had to him was not mutual. The idea that dogs are loyal by default is a bit of a misunderstanding. They can be fickle too and to him maybe you were just his walking food and water dispenser. If you get him back, and I hope you at least try to convince your family to let him back in, try to connect more with him and train him to listen to your commands. You're the leader and should follow so you two have a pack thing going on.

Sorry about the loss of your other dog but we can't focus on the dead too much when we lose them, we have to carry on and remember life continues.
Like I said I hope you can get your dog back in and TRY to convince your family to be more patient with your dog until you can properly train him.
Good luck.

I do not know you or how you care for your dog so I am simply going to suggest what is the most common problem... In the vast majority of cases where a dog is misbehaving in any way the solution is long walks every single day and even beyond that activating a dogs brain with games and tricks that keep them thinking.

I am not saying that everyone has to walk their dog for hours every day and activate them with tracking games or teaching them to pull or chase or jump or run or herd animals or whatever their specific breed may have been bred for - but I am saying that when problems appear it is very often because that specific individual dog is not getting activated enough - brain or body.

So take your dog for really long walks. Try to figure out which breeds it may be closest to, maybe play some games to see if it likes to fetch, to hunt, to search, to herd, and then based on what it seems most interested in find a way - a game or a job - that will let it use its brain to do what its instincts tell it to do. This will tire the dogs body out, it will tire the dogs brain out, and will make it much happier and nicer to be around when you just want to relax and have a nice companion at the end of the day.

Good luck!

Disclaimer: I'm not a vet or otherwise a specialist.

Dogs are intelligent animals. They can tell who their friends are. Your dog knows that you took care of him. He won't forget that. Not in one day, not ever. He doesn't see what you did as abandoning him. In some ways, it's like you were a parent, and you set him free to live on his own. The immediate need for him to be around you at all times is gone; he's free to form his own pack. Right now, socializing with other dogs is natural.

Be around him. Let him see that you're still there and hear your voice. And give him enough time for him to figure things out. After that, two things can happen. One, he'll decide that he wants to be home. In that case, one day you'll be walking around and he'll come to you. Two, maybe he's just a born alpha and he'll always prefer living in an actual dog pack. If so, you'll have to part with him like parents eventually need to part with their adult children. And that hurts, but he'll always love you, just as you'll always love him; you two are family. ;)

In any case, you definitely didn't mess him up. Maybe he's just more into living like an adult stray than like a pet. Don't blame yourself for it. He's definitely happy the way he is now. If he wasn't, he'd put effort into coming back.

Can you at least keep feeding him? Maybe not near the houses (I know people love to poison them), but at a spot nearby.
That's all I'm going to say.

Can you post a pic or video of the dog?