I have often wondered what happened to the heroines that James Bond ended up with at the end of Ian Fleming’s novels. It is a long time since I read the books but I seem to recall that Bond fell in love with all of them. I like to think that there must have been a breakup scene between one book and the next. Two died (Vesper Lynd and Tracy Draco) so any problem Bond might have had with dissolving his relationship with those were resolved. But it seems more likely he just abandons them without so much as a goodbye when he begins a new adventure.
Another hero I was a fan of at about the same time was the Leslie Charteris character, Simon Templar, better known as the Saint. Templar seemed to treat his women in the same manner as Bond but one heroine, Patricia Holm, appeared as his long standing girlfriend in some of the novels despite the fact that he had other lovers in between stories. Again, like the Bond girls, I have no idea how he broke up with these beautiful women, as they were always described as being beautiful. It must have been hard on all concerned.
The above are only a few examples of heroines from two popular thriller writers and their effect on me is such that I may have regarded them as models for female characters in my own stories. But the problem of how to resolve what happens to them at the end of a story remains. I remember watching the TV western series Bonanza as a teenager in the 1960s and pitying the women who fell in love with Adam, Hoss, Little Joe or even Ben (Pa) Cartwright for they were most always doomed to die.
I have been tempted to develop some of my books into a series. Such series can help to develop a fan base and become very profitable so it is extremely tempting. But I am not a great fan of sequels. My heroes tend to be men and what to do about their heroines will remain a problem that I have a difficulty in grappling with.