ok i know that sounds bad but hear me out

i've (26F) had my dog basil (3F) for about a year now. i got her from a shelter and i knew she had been surrendered by her previous owner (she had a limp there which turned out to be an improperly healed fracture). i had kinda gotten the idea that her previous owner either didn't want her anymore because of the injury or because they couldn't afford to take her to the vet. i've helped her recover from it and she's been able to walk around just fine now for a few months (although she does still have her limp sometimes when she runs).

this is the part im conflicted about. someone claiming to be basil's previous owner (??M) messaged me on insta yesterday. i dont think the shelter would have given him my personal information so he mustve just seen one of my pictures of basil somehow. but he wants her back. he showed me some of his pictures of her and it really does look like her. he said he's more financially stable now and the only reason he surrendered her in the first place was because he couldnt afford the vet bill. i really don't know what to do here. i do not want to give up basil. i love her so much and she is such a sweet dog. but i keep thinking about what i would do if i was in that guy's situation. i'd feel horrible too :( but i have really bonded with basil especially in helping her recover from her injury. i havent responded yet but im leaning towards saying no. im worried that he'll guilt trip me though. WIBTA if i didn't give her back?