Hey Dani
With bettas, the males have the extremely long fins that flare up when they're getting aggressive. In the red female betta picture above, you can see that her top fin is more proportional to the rest of her body....and though they still flare that small fin when they're not happy, it doesn't take up the whole tank. I started calling her Sweet Pea when she started displaying unanticipated affectionate behavior
Sounds like you know from experience that animals get attached to you for sometimes unexplained reasons. I started keeping fish because of the reasons you mentioned...not being as able to take care of furry pets.
With Jo, I'm not really sure if male or female...so I picked a gender-neutral name, in case my assumption that he was male was wrong...haha. He's named after a singing partner that I had back in the 90's, Joanne, a Puerto Rican soul singer who had studied the techniques of old blues singers until she had it down perfectly....her favorite was Sarah Vaughan...because of her ability to mimic the horn with her voice. It was totally foreign to me, and to music ministry at the time, and we had great fun, and laughed a lot, when she'd try to pass on that technique to me. She was a barrel of laughs. She passed away suddenly after some battles with her health, and possible liver cancer. A diagnosis was being pursued when she just passed in her sleep one night. I certainly missed her humor and zest for life....and I named my little fish Jo, to remember each day the fun we had.
In case you're like I was, and have no idea about the techniques of old jazz and blues singers, here's a sample of Sarah Vaughan being a "trumpet"....and imagine Jo stopping the song, and saying to you, "now do that...."