New Puppy causing issues with smaller, older dog. Don't know if we should keep him.

Hi,
I joined to post this question as my SO and I are at wits end and we don't know what to do. We have 13-week old puppy that we brought home about 8 days ago. He's a Shepherd\Lab cross and seems to be a happy, playful and very rambunctious little guy. Our other dog is a 14 year old Chihuahua cross. She is generally pretty anti-social with other dogs but we've had 2 previous large-breed dogs (both older rescues) that she has co-existed with without any problems. The issue is that the new puppy wants to play with her SO BADLY that he generally loses his mind whenever he's near her, and due to the fact that he is already about 3X her weight and is all paws, we're afraid he's going to inadvertently hurt her. She is not a playful-type dog, and will actually leap and bite at him, but he just stands there when she does that, so we don't think he'd intentionally hurt her, but she's not in great physical health and the few times we've tried to get them together, he's all over her, pawing and jumping around. At the moment we have our house divided into "his and her" spaces, but we cant keep living this way. Does anyone have any experience with this kind of situation? Any tricks or methods we could try to get them to coexist? If we cant solve this we're going to likely end up having to rehome him. It's just not fair for her (and us) to be cordoned off in what was her (our) home.


Thanks all.