At the time of drawing this pic, I had completely different ideas of how the kids grew up, and who went out with who. But time passes and new ideas come and go, so now I have a completely new take on how they grew up and their social lives.
As of today, I have Bart paired up with Allison, but they don't get together until Bart's in his late teens, (around 18-20). Before that, he had a reasonably long relationship (for a teen, anyway) with Terri, which was an off-and-on thing that spanned most of his adolescence. In-between these periods, Bart dated quite a number of girls in his time, and Becky, Anya and Janey are some of them, as well as Sherri more than once. (The Twins aren't selfish. ).
Like most teen boys, he was naturally too emotionally immature to just settle on one stable relationship, at least until his later teens, when he did with Terri, and then later Allison.