Unless the sim has the heartbreaker lifetime wish, commitment issues sims don't necessarily express it in romance matters, aside from needing a higher relationship to be willing to go steady or get engaged or married to begin with. I noticed when I played Marc Brandt in Twinbrook, when I had him in a good relationship, he never rolled antagonistic or breakup wishes. He did wish to quit his job more than once, however, and I noticed if he got frustrated with something (like when he got himself singed fixing the TV) he would roll a wish to get rid of it. So it could be that a commitment issues sim is just less likely to stick with something that's turning out to be more trouble than they feel it's worth.
