Part 5 contains the abusive relationship Gabriel has had with a dom. There is dub-con in it but not very detailed. also a lot of gaslighting (making the other person feel and believe like they are at fault for the things happening to them), belittling and just general shitty things to do to another person who puts trust in you. there is also non-con body modification in there.
none of the gritty stuff is detailed, though… like there is not a detailed description of how he is getting pierced in there.
that said; you can easily avoid all that stuff by just not reading the cursive part in chapter 5 🙂