Glad the dude walked away without drama. Second the advice to change your locks - this guy is not trustworthy and he may have swiped one of your spare keys at some point and made a copy, if you didn't give him a copy outright.I flat out asked my BF if he kicked Copper. He said no. He said he's always told me if he's stepped on his tail or paw by accident, which he has done. However, he was very unconvincing and unusually calm for being accused of animal cruelty.
Most people exhibit an outrage response if someone suggests to them that they have done violence against another entity. The fact that 1) he was calm and 2) you said he was unconvincing, combined with the fact that he actually left the relationship, really points to him having done it.
I'm currently dating a guy (have been for 3.5 years) who is mildly allergic to cats. He's incredibly nice and will voluntarily interact with my cats. If we were to move in together I'd have to keep the cats in one of the rooms and maybe build an enclosure in the yard outside the window, so they'd have space, but it could be done. "Allergic to cats" isn't the trait to keep an eye and an ear out for in new partners. It's whatever personality traits your ex displayed in the 7 months that you knew him. Think back with that 20/20 hindsight, and you might start to notice little telltales that indicated he would be abusive - word choice, reaction or lack thereof in situations that call for empathy, overly affected or flat affect, whatever. Even if you didn't consciously notice them, your subconscious did, so trust your gut feelings around partners in the future. Even if you can't articulate something that seems 'off' about a guy, if it's 'just a feeling' - trust it. Trust yourself. Glad you and Copper are okay. Good luck in the future!