I just adopted a new 10 month old puppy. He was rescued and has fears of being abandoned so he can't handle being alone. Last night we went out for a few hours and he went to the bathroom in his crate, even though he is house trained. He was crying so loudly when we opened the door. He also cries is we leave him alone in his crate and close our bedroom door. How can we help him get use to being alone, without upsetting him so much?

It is a very very slow process but it can be done.

You need to have the puppy in a crate or in the house and leave.

Find out how long it takes for the pup to start crying by listening at the door. It might be a minute, it could be 2 seconds.
For the purpose of explaining we will say it was 10 seconds.

Now come back in for a while and act normal.

Then leave again and wait outside for 10 seconds and come back in. Only come back in if the pup isn't crying and give her lots of praise.
If she is crying before it I time to go back in, pop your head through the door and give her a gowly 'no' and leave again.

Do this repeatedly over a few weeks, making each time you leave longer and longer. Praising her when you come back in for not crying.

Provide plenty of toys and stimulation while you are away.
Kongs are great as they can be filled with food and keep a dog occupied for hours.

Always make sure there is fresh water and a snuggly blanket.

Where do you keep the crate?
It needs to be somewhere to pup feels safe and secure.
I put a blanket over my crates and leave only the front open so they can see out.