Hello, I have a wonderful neutered male, 2 year old Cavalier king charles named Bentley. Bentley Loves people, kids, other dogs, cats, everything and every one. Perhapes he has been a bit spoiled. He has been well socialized often taking dog park trips, took a socialization class as a pup.. we work on issues with a trainer as they come up.. he had been humping from time to time at the dog park so we were working through that. I love Bentley so much have wanted to add a second cavalier king charles for some time. We went meeting dogs and Bentley got on fine with them all on their territory and on neutral territory. We finally choose to go with an 8 week old female black and tan cavalier from the same breeder we got Bentley from but different parents (the dogs are actually co owned) They did fine on neutral territory but as soon as we got in the house Bentley was mad.. I have never seen him like that, Barking, snarling, at her. I separated them and have been trying to work things out with them gradually. It has only been a couple of days of course. He also tries to push her under him and hump her, but she wiggles out as a small 4 lb puppy will, and he gets annoyed about that too. I can tell him "SIT" and it seems to redirect him. I am so in love with my new girl who I have named Velvet, already, so I need to make things work out. Bentley seems fine with her when they go out and potty, or are just calm together, sometimes something will set him off though, like if she gets too comfy on my lap he will start growl barking at her and acting like he might nip her but doesn't actually do it. though she does have slobber on her after. If she moves to my husbands lap he goes over to him and does the same reaction. then I have to separate them. Toys.. forget it, he will not let her have her toys or his. If they are just walking around together they seem fine.. but he does not like her getting playful or too snuggely with us.. he also gets mad if he notices her mouthing. (teething pups of course require that training) it is hard not to have him notice as we are correcting her. I am trying to keep things equal, equal attention, when they are together (she is crated a lot for house training anyways) They potty together and both get a treat, teaching her sit if he is there and sits they both get a treat. Both get petted at the same time together, and when Velvet went to the vet today I took Bentley along. These were all tips from the trainer I go to. I just have never seen this sweet doggie boy of mine so bent out of shape at another living thing. I just want re assurance that others have been through this, and had it all work out in the end, and give me tips as to what worked for them! I keep reading mixed advice on what to do in this situation so I am not sure what to do. I am leashing them for interactions right now of course for safety reasons and I am of course only allowing closely supervised play. Velvet also has a safe play area that I gated off with an xpen, where her crate is. They are eating in the same room, But Bentley does not care much about food anyways, never had a food aggression problem there.