Is it permissible to supplicate for reunion with the first girl after marrying another, knowing the difficulty of living with and accepting the second wife?

If the aforementioned girl is righteous and beautiful, then it is preferable to complete the marriage with her, due to the hadith: "A woman is married for four reasons... so choose the religious one, and you will prosper." She combines both religiosity and beauty. If the first girl is religious and of good character, there is no harm in supplicating for facilitating marriage to her as a second wife if you are capable of being just; otherwise, there is no good in that. Do not let thinking about her be an obstacle to your marriage or to treating your current wife well.