What you just described sounds most likely to be related to auric magick. It is not a "spell" in the most technical aspect, but he was simply programming his aura to cause you to feel an uncontrollable desire for him. You can find out more about auric programming by Goggling "how to program your aura" (quotes not necessary), or go here: http://www.angelfire.com/empire/serpentis666/AURA.html. Now, I shall give a brief description of how this "Aura Magick" is used:
The person sends out their aura to do their bidding via programming.
If your aura happens to be weaker than theirs, or you are not expecting anything like what happened (i.e.: you have no clue what "aura" is, you know about aura but not "magick," etc.), then this program will more than likely succeed, especially if the person doing it is very passionate about it.
Aura programming is not like normal "love spells," in that it does not normally run the risk of backfiring on the programmer (with certain, if not all, love spells, the inexperienced person may carelessly use this and they will only fall more deeply in love [to the point of obsession even] with their "victim," but there will be little change if any to the programmed's feelings.).
Aura magick is not only used for love, there are a variety of things it can be used for, even killing.
Due to this fact, he sort of "bonded" with you, this is why you had these crazy, odd feelings, and unfortunately that also came with the side effect of extreme, irrational depression. Once he "released" you, your mind and soul was no longer bonded with you, so you went back to your "old self."
There is one other rational possibility that could have happened: that is that your ex-boyfriend/lover was an Incubus, this is highly unlikely, but possible, in theory. This can be inferred from the phrase "I release you," normally, incubi, when causing a ladies to have mad desire for them use the French phrase, "Je T'aime (French for 'I love you')," to "capture" their victims. Oh, and if I am wrong about this particular matter on incubi, let me know everyone.
I sincerely hope this helped to provide you with some cloture. If not, I apologize.