I have noticed that sometimes my sim will have an interest and it changes or that other sim changes, if I make them only friends then try again sometimes it works out (sometimes it doesnt) so there may be some compatability, I think sims change a bit over time too, at least it seems like that to me. I know I can delete my sim from a game and put her back in and she wont act the same way, have same love interests (except for a small few who seem to always have the same one even if i make 100 new games with them in it), good luck
