In the Fire and Blood book, Baela moves on very quickly after Jacaerys’ death and takes several lovers from Dragonstone. She marries Alyn a year later. Looks like House of the Dragon is erasing the lovers Baela took and going straight to her marriage.
House of the Dragon generally likes to erase many plot lines.
So, of course, they don't have time to explore them in more detail, and I think in this case, this is the best plot move for Baela, and a very logical one. The war is in full swing. Jace dies, the whole situation is precarious, and of course, marriage is inevitable to strengthen rights and power. I'm already somewhat accepting thanks to Bethany and Abubakar's shared content (even though it wasn't much, the seeds have been sown). I'm certainly interested in how they'll portray this. Baela has a strong character and has held her own so far, but Jace's death will definitely affect her. And the thought that she will ultimately be forced to marry Alyn is quite bittersweet. But I hope Alyn proves himself to be a rational and understanding man. And if there's no love there, then at least respect (in the books, they have an unhappy marriage with his infidelity, but who knows how the show will go, although I think they'll never show that).
I'm more interested in what they'll bring to Rhaena. According to the books, she has two marriages. The second was to Garmund Hightower, with whom she had six children, and their marriage is described as happy. And given the rumors and gossip about season 3, it's allegedly (SPOILERS) that Rhaena will have an affair with Gwayne Hightower. I think this is more of a fan fantasy, but I wouldn't be surprised if the show actually did it.