How Can I Make Him Take a Bottle.....

The only thing I can think of to do, is to either try to breasfeed him before you leave him ( if possible), or if not you may have to have him take a bottle once or twice a week at home so he is used to it on the occassion you need to leave him with a sitter.

You can try different bottles, and have them squirt a little milk in his mouth so he knows what it is. You should not bottle him, so maybe every other evening have dad give him a bottle and you just pump.

I would try and have someone bottle feed him at least once a week or so to remind him that bottles are ok too. To get him back "on" it, try pumping an ounce or so and imediately give it to your husband (and you leave) to feed your son. He's most likely to take a bit when he is hungry and it is very fresh.

Can you just make plans to take him with you instead of leaving him with a sitter? My daughter is almost 18 months and we practice attachment parenting and I just left her for an hour and a half with her daddy for the first time last week.
Not judging, please don't take it that way... just curious if there would be an alternative to having to leave him.