in addition to Austin's answer, I would say that the word 'boresome' is infrequently seen. Personally, I'd use "boring" instead.

Yes very much so. Bothersome describes an irritating person or thing, while boresome is something that is not interesting, exciting or fun. Examples Doing my homework is so boresome. Watching these slow documentaries is so boresome. These bugs are so bothersome. The barking dog is so bothersome, while I try to concentrate.

Yeah, I cant say I have ever seen the word 'boresome' used - ever. Use 'boring' instead.