Ugh, 'possessive werewolf mate' is my absolute favorite niche to hate-read sometimes. The dynamic walks such a fine line between thrilling and completely obnoxious. For a free option that actually nails the romance, you can't go wrong with 'Fate's Captive' on Wattpad or Radish. The author, Kaela Rivers, really gets the push-pull right. The male lead is utterly feral about his claimed mate, but the female protagonist has this steel core that forces him to grovel and earn her trust in a way that feels satisfying, not Stockholm-syndrome-y.
A lot of the free stuff on serial apps updates chapter by chapter, which is great for the slow-burn tension. You get that weekly hit of 'will they or won't they' as the bond snaps into place. The downside is you might hit a paywall for early access to new chapters, but if you're patient, you can read the whole thing free. I find the community comments on those platforms half the fun, everyone screaming at the characters.
Just steer clear of anything where the 'possession' is just verbal abuse with fur. The good ones use the supernatural bond to explore devotion, not control.