You can call him whatever you want but good luck having anyone NOT look down on you for doing so seeing as how he is still legally married to another woman and until their divorce is finalized you won't be getting anywhere close to marrying him.
You are gonna have a bunch of people tell ya hell no but I thik it is a personal preference. I call my SO that when introducing him in public because that is what he is. We plan to get married when my divorce is final. An engagment is not a legal bidding filed in court thing.
He is still married and the divorce has not been finalized yet. Can I still call him my fiancé or boyfriend until everything goes through?