I suspect that you have a very small sample of married BLs in your acquaintance. You could ask as many straight people about their marriages and find them just as unsuccessful. Marriage is hard for any couple and lots don't make it. My point is... the testimonies you have heard (including mine) are valuable anecdotally, but surely are insufficient to make solid conclusions from.

To answer your question: "What would you tell someone to avoid having the same troubles you have had with marriage as a BL?"

Above all, accept your sexuality as you find it. Don't try and force change on yourself. You're attracted to whom your attracted... just accept that.

Secondly, I don't believe it's a betrayal of your wife if she doesn't know the details of your fantasy life and it's probably going to hurt her a lot if you get into the nitty gritty (I'm sure this is true for as many straight guys as it is for BLs). If you need to use fantasy as an aid to sex it doesn't make you a bad husband. As long as she's the one you're bedding in the real world and you stay faithful to her in that regard, that's what matters. You can love her in a million ways without ever having to be attracted to her physically.

Lastly, if you are having problems dealing with the sexual side of your marriage find someone other than your wife to unload on and be accountable to.

Blessings
Cat.