Understanding of years-old multifaceted hydrogen-assisted damage evolution necessitates efforts to model the coupled diffusion-mechanics response in metallic materials. Informed by the dislocation-hydrogen interactions, understood earlier via experiments and/or multi-scale modeling techniques, this work presents a dislocation density-based crystal plasticity model coupled with a hydrogen diffusion/trapping model to simulate the hydrogen-assisted deformation and failure under the HELP mechanism of hydrogen embrittlement. The important role of hydrogen on dislocation multiplication, annihilation and dislocation interaction weakening are included in the presented framework. Two possible scenarios under HELP mechanism, leading to H-induced macroscopic softening or hardening as a result of trade-off between the hydrogen-induced weakening of dislocation interactions and hydrogen-induced increased dislocation density emerges from the simulation studies. These finding points towards the inevitable role of HELP mechanism to cause early failure in metals either working independently or in support with additional mechanisms.