At the end of the day, I've honestly tried everything I could to make/keep him happy and spent all my patience - and nearly my sanity - to keep this relationship together; but the whole time it felt one-sided/like I was the only one really trying.
I think you've probably made a very astute analysis of your relationship right there.
The question I might ask myself after realizing something like that is -- "is this the kind of relationship I want? Do I want to continue giving and giving and giving and getting nothing in return? Even if he did come back?"
This also sounded very familiar to me:
I supported him in literally every way you can think of (got him a big screen TV, found his new/awesome apartment closer to his job, took him to the ER when he needed stitches, got him a pure breed bengal cat so he wouldn't be lonely when I left for grad school, took him on an all expense paid week-long trip to Universal in Orlando because he had never been, on trips to the beach and mountains, etc) to show him how much I cared. I also, worked hard to maintain my body, looks, education and job to try to be a girlfriend he could be proud of/want to keep.
What I've learned after I left that high-maintenance exhausting relationship with an alcoholic is this:
A good relationship doesn't require that much work.
Any relationship requires commitment and work. But when you're exhausting yourself like you did (and like I did in my first marriage), you're not working on a
relationship. You're trying to
make someone else happy (as you said).
And you can't. It's not possible to
make someone else happy. Their feelings are their responsibility.