Hey sweetie. Nothing new. God awful. Don't recommend it
Ok, you say, let's look at this from an LBS. I take that to mean an LBS on DB who WANTS to reconcile their marriage. That means take me and my situation out of the equation. Take the past out of the equation. AND, stop mind reading and looking for or assuming a motive. The idea is that you want back in.
You are trying to find out an answer while protecting yourself. That won't work. Ever. Take my word for it, I could write a book on it. You have 2 choices: 1) You make yourself vulnerable and take the leap without looking for his motive OR 2) You protect yourself with the understanding that there really is no way to reconcile this thing. Believe me, I am not here to judge you because I took option 2. So I will not beat you up because I believe that it eventually gets to that. Are you there? If you are not there, then the walls will need to come down with blind faith. Faith is believing in something when there is no proof that it is true. So while I understand your reservations (I really, really understand), you need to make that decision. And it must be for YOU. Not for him. Not for son. Not for a piece of paper. For you.
Now, from an outsiders observations, it looks like he is trying. And maybe he wants sex, but let's be honest, that's not too difficult to get anywhere. He wants sex from you. Now, that's interesting... hmmmm...