painfully, hon, I'm sorry this happened and I know exactly how you feel because this has happened to me many times. Trying to figure out why he has done what he has done is digging your hole deeper. This is not a "relapse" or mental illness or necessarily alcoholism, this is who he IS. And it has nothing to do with you. I also have done those drive-bys and I can tell you it was the worst time in my life. Later, I realized it was pure obsession. I didn't know what else to do. It was making me crazy not knowing where he was. I would drive by ALL NIGHT.
Not to make light of your situation but there is a certain truth to this joke: Q: How can you tell two alcoholics are dating? A: There's a moving van in one of their driveways.
Have you read Codependent No More? If not, please check it out. You can get it at the library or for cheap on Amazon.
(((hugs)))