It's really not uncommon for this to happen. You and your crush are both drawn to the same man (your boyfriend), and probably share some history, values, a sense of humour and so on. And being on holiday and enjoying yourselves will have been a lot of fun and probably a lot of laughs as well.
You probably need to accept that this scenario is one which is highly likely to arise from time to time. Why would you not find each other attractive - and even enjoy a little flirtatious behaviour?
Feeling attracted to the same person who is attracted to you is a potent cocktail - it is pleasurable and exciting and enticing - and in a situation like yours it is very important to look carefully at how you choose to respond.
The real issue is one of intent. You can pursue these feelings, or you can accept them for what they are - in relation to your current committed relationship.
Dr Gary Lewandowski author of the blog The Science of Relationships puts it this way: "A process known as 'derogating alternatives' helps us maintain our commitment to our original relationship - for example my single friends might think that Anne Hathaway's hot, but since I am married I tend to think her big teeth make her unattractive."
You know what is innocent and you know what is not. Much depends on your relationship with your boyfriend whom you say that you love. He has obviously earned your love for a whole lot of reasons. Some innocent flirting will no doubt have your boyfriend enjoying the fact that his friends find you attractive too. Flirting with intent to take it further is going to be playing with fire and it is a good idea to take a deep breath and look very carefully at your feelings.
First off you need to think about how you would feel if the shoe was on the other foot and your boyfriend was falling for one of your friends. Read your letter again and imagine your boyfriend wrote it about one of your friends - and how you would feel if he acted on that attraction. Related to that is what you actually think in cooler moments about a man who would go behind his mate's back. Does that fit with your value system?
All of us, when we are relaxed and are on holiday and having fun, show our very best side - and compared to the weeks at work and all the other more mundane aspects of life that we share with our partners - the holiday can be a real aphrodisiac and make "real" life feel rather dull by comparison.
Feeling attracted and attractive means you are alive and vibrant and responsive - but you don't have to let your options be dictated by these feelings.
However, if you find that your feelings are very serious - then there is a complicated situation and one which you need to consider carefully. What is happening in your current relationship? Is it not really working for you any more? Have you become resentful about some issues and have you tried to work these out with your boyfriend?
If the real reason behind your crush is that something is not right in your relationship then it is time to make some decisions to explore your commitment and whether you can remain in it. To pretend all is well when it is not, is very unfair to your boyfriend.
If you decide that your relationship with your boyfriend has run its course, then the next step will be finding a sensitive way to break this to your partner and to explain that you need to continue on your journey without him. If it is over, then it may be because you have grown apart. You would certainly be wise, if this is the case, to be very cautious about any involvement with his friend. And if in the end, you do end up exploring this new relationship, it must be conveyed to your boyfriend who would then be your ex-partner, that you began to experience your deeper feelings only once you were single again. He will be hurt but his emotions would be more manageable than if he knew you had cheated on him.
So recognise there are issues here - firstly the joy of being happy and attracted and attractive, along with the more sober and serious issue of cheating and creating a lot of hurt and pain - and possibly losing your partner and your self respect. The third point is considering carefully whether your current relationship is finished - and then - and only then - examining this new attraction from an honest and transparent position.