Hi, S..
My 10-month-old, Zoe, was exclusive breastfed for the first 3 months, so when it came to switching over to bottles to allow someone else to watch her, it was difficult.
The only things I can suggest are you try stcking to one type of bottle and nipple, ensuring you have the right flow for his age, and that you try dropping one of his nursings with you and you attempt feed him with the bottle. Also, be diligent.
This seemed to work the best for me. When I got my daughter used to the fact that I was feeding her with a bottle, it was much easier to have someone else feed her. Realize, it took about three weeks before we made any progress. Keep trying. Some babies are easier to ease into bottle feedings and some will fight it.
I hope this helps. Good luck!
All the best,
E.