I don't believe it is always bad/wrong/avoidable to stay in touch or even become friends. I think a lot of consideration and care should be put into it and still things might go differently than anticipated. So I'm with DP on this. But I also worry if the idea of it becomes too much of an obsession, that might point into the direction of too little balance. That's why I suggested trying to find support and relationships and love from other people as well. If one person is the only source of it all, it doesn't sound good and maintainable.