Jacob, despite experiencing the excruciating pain from the Cursed Immortality, this pain was still not something that he could take with a grain of salt.
Furthermore, Masha wasn't just done after making only one stroke, but she was just getting started, and she even had this crazy sadistic look in her eyes as she stroked Jacob's back, and watching him tremble and groan in pain gave her pleasure. She was not different from an Evil Witch at this moment.
However, as painful as it was, Jacob endured with everything he had and focused all those pain on his hatred for being so powerless despite everything he had done to reach to this point.
Despite enduring so much pain and being so much meticulous, he still ended up captured by a bunch of outlaws, and now to survive, he needed to be a slave. He never wanted to experience this sort of feeling after Decker's lab, but here he was, forced to walk on the same road again. He wasn't angry at anyone but himself for still being so powerless.
