Why can't my wife support my decisions at all?

I know it's long, but please consider answering. I would be so grateful. We've been together a few years and had our ups and downs. Sometimes she's great and I love her very much. I got out of school and am in the process of finding work. We had some problems last year that involved her flirting with various men, especially with a man at her work. She tore me down when I found out (she was apologetic at first but it didn't last), flirting more at random (delivery guys, repair men, etc.) and insulting me with jokes about my manhood. She eventually showed too much of herself to the young guy down the street (19 or 20 yrs old) and he came over while she was gardening at the side of the house in less than enough clothes. She sat and chatted with him about sports and his soccer team while I fumed inside. We talked about her actions many times and she eventually said it was because she felt I hadn't given her the lifestyle she expected when we met. She expected a big house and three kids by now (she turned 30 recently). But those times when I have worked hard at my part time job during school or spent hours studying, she complained she felt neglected. Lately, I was depressed and lacked motivation and graduation was not good. I thought she might leave at any time. On the job front, many of my classmates have had trouble finding work, but recently I felt really invigorated and motivated. I went downstairs today and basically told my wife that "I'm going to get out there and show these people they can't hold me back." I felt great for the first time in weeks. She immediately turned on me, told me I'm being a jerk and that my only goal should be to be nice to others. I felt like for once, after everything that happened, she could have been happy I had my drive back. She's told me plenty of times to get out there and do what you need. Now when I've been fired up, she says I'm a jerk. When she was looking for her job last month, she was offered a lousy position at a school in a bad part of town, which treated the kids like fools. My wife said she wanted to teach kids to achieve in life, and so held out for another job though she did not know if she would get one. She did, and I supported her in all this. But I'm in Catch-22 with her all the time. At lunch yesterday she said her grandfather had eaten her food (he lives with us). I said I would ask him not to eat her food from the fridge, she said that I was being rude and should respect her grandfather. Today at lunch, same complaint, he had eaten her food again. I said nothing, and so she got angry at me saying I should solve the problem. What was I supposed to do? It bothers me that any answer I have is the wrong answer, whether little issues or big ones. It bothers me that because I don't give her everything she wants she treats me like crap. We have all the basics, she wants extras. Why can't she support me when I need it? Why is everything I do wrong?