Firstly, you know it is not the milk cause he will drink it from the breast. Do you know if it is the bottle, maybe try another (I tried many but the one I finally succeeded with was NUK). ALso if possible try and get someone else (as you said you have) to offer the bottle, baby might associate you with the breast. Good idea is to try when you are home but someone else (ie, husband/partner/helper etc) offer bottle so you can monitor baby's reaction too.
I know it sounds silly but I think the number one rule is to keep calm. Baby will sense if you are distressed about it. Talk to your baby and tell him what you are doing before offering the bottle. With my daughter she would just cry and cry and cry when I put the bottle in her mouth, even when I tried for around one hour. I found I was beginning to stress. After three weeks of no success, I did some homework and then I tried to (pretend) to ignore her. I offered her the bottle one day with EBM in it, and pretended to watch television so I was not watching her. I continued to keep the bottle in her mouth the whole time. She cried and sooked for around 5 minutes and then she began to drink from it. I was so happy. I found she drank around half the bottle (around 100ml) and then began to lose interest again. I did the same thing (watching television while holding her with bottle in her mouth) and she began drinking again, drinking a total of 210ml. I think she realised she wasn't getting attention. I know it sounds simple but it did work. Once I had success, I made sure I offered her a bottle of EBM once a day to build her confidence, and had no problems after that. I then graduated to a mix of formula and EBM. Another method one of my friends used, who also had the same problem was to place her baby in a baby swing she had with lights and toys and music for distraction whilst offering the bottle. You could try this as well.
Bear in mind to try and avoid getting bubs dehydrated, so if they don't take a bottle at one feed, try and offer the breast again next feed. Some parents think the way to get a baby to bottle feed is to just refuse breast feeding, thinking they will eventually take the bottle. I wouldn't recommend this, just try to persist say once a day with a bottle and he will eventually try it.
Good luck (I definately know what you are going through and it can be quite stressful). Let me know if you intend to wean to formula and I can recommend some other techniques, as offering a full bottle of formula to my girl really put her of the bottle all together and this is what caused the above. All the best!