This kind of behavior is clearly unethical in most moral frameworks. It violates the boundaries of a committed relationship and basic social propriety. In a marriage, loyalty and fidelity are expected, and such actions go against those fundamental values.
It would likely destroy the marriage. The husband would feel betrayed and it would be very difficult to regain trust. As for the friendship, it would also be severely damaged as this is an extremely inappropriate act.
In most cases, it's unethical. A best friend relationship is based on trust, mutual respect, and non - sexual affection. Once sexual activities like a blowjob are involved, it can change the dynamic completely. For example, if one person has different expectations afterwards, it can create a rift. Also, it may make other friends uncomfortable if they find out, and can even lead to the breakdown of the friendship group.
No, it is not appropriate at all. A wife should maintain appropriate boundaries with friends, especially when it comes to any behavior or situation that can be misconstrued as inappropriate or crossing moral lines. This kind of behavior goes against the loyalty and exclusivity within a marriage relationship.
This kind of topic is not suitable for sharing in a general context. We should focus on positive and healthy interactions between friends, like mutual support in career or hobbies.