Useful advices do come in papers, yet people don’t follow them:
Some of the reasons men stay in a marriage is that they have some intimacy in the form of shared experience and companionship with their wives, and if their reasons for being in an external relationship is for the sex, then they’re not going to leave their marriages. That’s not enough.
So if you want to find out how he really feels, draw some boundaries.
Say that you love him, that you have had a great time, but that you need some action if the relationship is going to continue.
There will always be young, unexperienced girls thinking it’ll be different for them. They have to see it to believe it.
Later in life, it’s just masochism.