There's a certain level of academic competition between me and my girlfriend, due to us both being very academically able and both of us having offers for the same course at the same first choice university. She always works harder than I do, and correspondingly outperforms me in virtually every test. Since I know that my doing worse than she does is entirely my fault for not working hard enough, rather than being jealous it just makes me feel lazy. If anything the overall effect on me is positive because I'm more motivated to work if there's someone I know who's better than me (because, frankly, beating everyone other than my girlfriend academically is usually pretty easy), and I'm not jealous because I'm happy for her sucess.