First question do you want her to fall in love with another apprentice or is a younger warrior okay? I do have Loveaffair in Fallclan who is fairly young. He is actually the son of Chestnutheart which is who Chestnutpaw was named after. XD also I just think his name is a giant red flag so it’s a big ironic in a situation like this.

Okay so looking at the ideas you listed. I don't think I could see Loveaffair dipping out on Chestnutpaw and any potential kits, but I could see maybe their relationship starts out very fiery. Like full of sunshine and rainbows type of relationship. Maybe Loveaffair tries to motivate Chestnutpaw about being a warrior, or want to try and support her dream somehow, and this is what causes her to maybe latch on to him? I feel in the beginning they enjoy each other's company. Maybe the first litter of kits was very much not planned, and they hadn't been together very long before she becomes pregnant. I could totally see both of them being nervous, partly freaked out because this is so not what they planned to do with their lives. Maybe they do a soul binding ceremony which is Fallclan's version of marriage. Wanting to be the best parents they can be for the litter. I'm all xD for traumatizing my characters, so maybe either one of the kits is stillborn or passes away within their first moon of life? Maybe both parents struggle with grief a little bit differently? Loveaffair throws himself into patrols and maybe Chestnutpaw falls into a dark depression and feels alone, because her mate is ignoring her. Maybe they have a close friend of theirs's or one of Chestnutpaw's siblings sets them down. To stake an intervention because they noticed Loveaffair is maybe ignoring Chestnutpaw and the kits? Maybe noticed Chestnutpaw hasn't been her normal self? Maybe the pair hash out their grievances and everything seem fine. A couple of moons go by their children are apprentices now maybe Chestnutpaw become pregnant with their second litter. I could see there being a lot of fear around this litter, due to them losing one of their kits in their first litter. Which this could go one of two ways. Either the parents stay together, grow old together and have a large thriving family. Or the pair realizes the love they once felt for each other isn't there anymore, but the pair agrees to co-parent their kids together.