On the Sacrifice to Learn Sorcery

Only the current one (unless you kill them, of course). Technically, the “sacrifice” is not some magical effect that removes your love for the person (or whatever feeling you have, you need Shun The Smiling Lady or Freedom Let’s Go for that). It’s the prerequisite to getting Sorcery, so you have to give up the relationship before you get the magical awakening. So you end the relationship in the same way you end any relationship using mundane means.

It’s like, say, disowning your son. Nothing prevents you from forgiving him later, but if you make enough trouble between the two of you in the process, it can be… difficult to reestablish it.

There’s no mention of anything supernatural making the thing unrecoverable. However, it does say that it will force a choice on the person and then goes on to list mundane examples of what that means. Heck, it doesn’t even say that the person has to lose any Intimacy (or other game mechanic specifics), but that it will force the person to choose between advancing their knowledge of Sorcery and their relationships, health, social status and temporal power. 

It’s all about realising that something is holding you back, and then giving it up so that you can go forward.

Realistically, it often works out the same. If you disown your son and kick him out of your house so he doesn’t distract you from sorcery and you can spend all his inheritance on spell research, then you’ve kind of crossed a line. Even if you, at some point, come to regret that action (which is unlikely, people have a tendency to self-justify their actions even, often especially, the horrible ones) convincing him to forgive you is going to be hard.

It’s like Immaculate initiation into Celestial Martial Arts. The Dragonblooded monk has to undergo a grueling process, slowly and surely giving up material comforts as he ascends the coils until he is eating rice and water and meditating all day and then… he learns an Enlightening Charm and that doesn’t matter anymore. The Dragonblooded can go on to be incredibly debauched and he will retain access to his Celestial Martial Arts.

Exalted is a game based around consequences, and one of the ways to make that matter is that the character has to be able to regret those actions they took. If a Sorcerer couldn’t regret his Sacrifices and try to regain them, it destroys half the drama of the Sacrifice in the first place.