The phases of He3 adsorbed on graphite are simulated by use of the Feynman path-integral Monte Carlo method. The fluid, commensurate solid, incommensurate solid, and reentrant fluid phases are found and are in agreement with the experimental phase diagram. The microscopic structure of the reentrant fluid is observed to be a striped domain-wall liquid and is consistent with a recent experimental interpretation and theoretical model. Larger-size systems are required for further quantitative analysis of the domain-wall liquid. © 1987 The American Physical Society.