WIBTA for trying to convince my roommate to give me her cat when I move out?

Now, this hasn't happened yet. But it's something I'm strongly considering doing. For context: My roommate has a cat, he is the sweetest creature I have ever met. However, she spends 0 time with him. When she is home, she is always in her room, where the cat is not allowed. The only real interaction she ever has with him is when she's feeding him, or when she's cleaning his litter (when she actually feels like doing that, lol). On the other end, I am in love with this cat. He spends all his time with me, as I make it a point to leave my door open for him at all times. He sleeps with me, hangs out with me daily, even when I'm not home he is always in my room. I think him and I have a very special bond due to the fact that he is otherwise quite neglected by his true owner. If it wasn't for me allowing him in to my space, he would be forced to live every day in our tiny common area that consists of just a small living room, and the bathroom. I'm moving out and getting a place with my boyfriend in April. While I'm very excited for this, I can't stop thinking about the cat, and how when I leave he will truly be by himself. I've been talking about it with my boyfriend, who also really loves this cat, and I think we're at somewhat of an understanding. The only real issue is that he already has a cat, and while "mine" is very good with other kitties, we aren't super sure where his stands. This is 100% an issue I'm willing to work through, however. I understand that asking someone for their pet can be like... a total dick move, but she genuinely does not spend any time with him, give him any affection, or even buy him toys (I've been doing that). Theres eveb been times where I have come home to him having barely any food, and empty (to the point if being dry) water bowl, and been the one to take care of him. I'm so worried for this cats well-being after I move out. I'm thinking about offering her money for him, and laying out a very detailed list of reasons why he's basically my cat already, and I think being separated from me will strongly decrease his quality of life. I'm just hoping I can do all of this in a way that is as tasteful as possible, while still maintaining friendship with her (at least until I move out). I just really love this cat. I've never felt more connected to an animal in my life (apart from my own pets), and I really want what's best for him...