My boyfriends dog

So usually I love animals and my dog is my best friend but recently I can't stand my boyfriends dog. I have a few reasons why I think I have recently started disliking her but I feel so guilty because I really wanted her to be like my dog like best friend #2. Anyway here's my reasons why
1. She doesn't seem happy when I come over, it feels like I come over and she's not happy about it 
2. She bit me while I was trying to pet her. 
3. She's old and my boyfriend pays for all of her old dog things and he says he's broke and can't see me, he lives 30 minutes away 
4. In the middle of our day I see him about twice a week he leaves to go walk her in the middle of our dates. So he either leaves or sometimes takes me but recently I don't wanna go because she's cutting my dates in half.
5. In the middle of watching movies together she comes up and kinda stares at me and I feel weird.
I feel like maybe another factor that comes into play is that she is a female dog so my boyfriend just leaving me in the middle of our dates for a female maybe gets to me idk. I just feel really shitty for not liking her.