She may be enjoying his attention, and maybe your brother is trying to do this on purpose to get your goat so to speak...If your wife has not given you any reason to worry about this or be suspicious of her, then maybe it is only in your mind. She denied it to you. Hopefully she is telling you the truth....Do you have any reason to think your wife is not or would not be completely loyal to you?
Even if you can't trust your loser brother...you should be able to trust your wife...unless she has given you reason to doubt her trust and faithfulness, I wouldn't get too overly concerned....
I would certainly hope your wife would tell him to hit the road if he ever did try something as low down as that....
I think you are just nervous about leaving for such a long stretch of time....Have someone look after your wife while you are away...do you have a sis or maybe mom could spend some time with her....
Try not to be too worried and bothered about the whole thing...I am sure the stress of leaving is just getting to you....have you asked her if she would be willing to join you in New York? That could be an option, and the two of you could have some much needed relaxation time when you are not working....
Good luck hon....I wish I could put your mind more at ease....(((((hugs))))......it is going to be alright....