My main issue is that it felt forced and was only served as fanservice to horny fans, instead of actual development with Cal

Drop hints that Merrin and Cal have feelings for each other; Have a canon tie-in book to FO introducing some imperial chick OC we hardly know about; Have her and Merrin be close with one another; Have her and Merrin have a sexy scene instead building up Merrin and Cal to have developed feelings for each other