Not everyone is so generous, especially since i've found out since her intentions were not as pure as that. The watch gift was 100% trying to buy affection I feel. Plus, this is a buddy, she's his work colleague. And yes I didn't like it - that's true. It seemed untoward and I was right, it was. I don't think that makes me a jealous or controlling person who will make him miserable.   
Also - I never said that anything sexual had happened between them nor have suspected this. I know it hasn't. I just feel she's disrespected our relationship by what she's said to me and how she's behaved.   
Also, I've never been jealous of an office lunch - the only reason I had a problem was because of all the inappropriate things she'd said to me the night before, if she hadn't have said those things, it would be in a completely different context and I wouldn't even bat an eyelid. If there were others involved, I wouldn't be so bothered and they'd have probably split the cost which is up to them, but it was the fact it was just between him and the girl in question, after he know what was said to me.