"On the table" means it is waiting to be picked up. In other words, the decision is pending. If it isn't on the table, then he's not even thinking about it.

No. "On the table", means something is being considered (think of proposals being "spread out" for everyone to "view" on a table around which everyone is sitting). "Marriage isn't even on the table" means that marriage is not an option; it will not be proposed under any circumstances.

Here it means that marriage has not yet been discussed.

婚姻 "压根就不在考虑范围之内”