Sorry to hear about your lost, I know you did your best to get him up and running. Sometimes baby dragons don't make it, due to some genetic default or overall failure to thrive. I am glad to hear your female is doing well, despite missing her old cage mate. But she will soon get over it as well.
If you do decide to get another beareded dragon, it would be best to house him/her alone especially for the first three months to ensure they are healthy (though I still recommend keeping them separate permanently).
You can get the vet to do a necropsy if you want to learn more about why he stopped eating and lost weight fast (from y our earlier posts it sounded like he lost weight fast over a short period of time, not sure how long y ou had him or if he was in poor health when y ou bought him).
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PHLdyPayne