advice please

So I recently adopted a dog, after talking to the shelter and being told he's great with other animals, is dewormed, up to date on shot, and doesn't have separation anxiety, I signed the papers and payed 105. He is truly a beautiful dog, so sweet and gentle with me and my boyfriend, but everything the shelter said was a complete lie. he has worms (we dewormed him again) is aggressive towards other dogs, and has severe separation anxiety (we've already lost our deposit and we've lived here 2 months). I feel so awful, I'm not one to take owning a dog lightly, and the last thing I want to do is bring him back but I don't know what else to do. he truly is a wonderful dog but I told the shelter I couldn't have a dog who has separation anxiety/aggression. I just feel terrible about the whole ordeal. I have no money for a trainer because I've spent like 500 already fixing what he's destroyed. I think I need to take him back but I'm heartbroken. I guess I just need some understanding and reassurance that I'm not a failure. I've never felt worse about a decision in my life and my boyfriend wants him gone 100

EDIT: I talked to my boyfriend after reading tons of stories about how dogs who get returned are pretty much immediately euthanized and I told him I'd do anything to help the dog adjust and he's upset but he accepted it. thank you ladies for your clear mindset in helping me make this decision