Sorry. Let me know if this is the correct scenario: Someone prepares food for another person who is married to someone else. They do not necessarily dine together. If so, it could or could not be alright. We need more information.
Agoins, it is not alright if the person in the relationship is offended by it. The offended should be open with the mate about feelings; and the mate (not the offended) should ask the cook to discontinue if he cares about the offended.
If it is his mother, sister or other relative, no issue. If it is a neighbor or friend from church dropping off a casserole to help because someone is sick, had a baby, lost a job, no issue, it is charity. If it is someone who is constantly giving him food to show she cares, there is a problem and she is violating boundaries.
If it's just a case of two co-workers having had a discussion about a particular dish (lasagna or whatever) in the past and the next time she or he made it they brought some into work to share....etc That wouldn't be a big deal to me. Having said that if it became "their daily routine" that would be out of the norm in my opinion. You might question their motives. One would have to believe it's impossible for the opposite sex to be platonic friends. No one would question it if two same sex people brought in leftovers to share (from time to time). Oddly enough if they were bringing in donuts, pizza, or food from a fast food joint no one would think anything of it. There's something about "homemade" that personalizes things especially if you believe food really is the way to a man's heart.
Why are people offended when others don't accept their faith? If you are sure, why be upset?Christ never tried to convince anyone to believe in him. He had a purpose, lived it out and people believed on the power of God...