If you thought the last person to poach your girl from you is your best friend, think again. She flirts with him often? Does she always insist you make him a part of your evening plans? See her mannerisms change the moment he joins both of you... as in, is she a little extra chatty, extra coy?
You are heading for trouble, my friend. But before you do anything nasty, to either of them, here are five reasons why she is behaving thus. No slugfest required here: play it smart and two of you will live "happily ever after".
1 They are both similar to each other
Look at it thus. You choose your friends, and your relationships, based on how compatible the person is with you. Chances are, then, that both of them are very similar to each other. May be she isn't thinking of jumping ship (yet!), but if you don't mend your manners soon, it won't take her long to get attracted to him. On the other hand, look at it positively: your friend need not be the only guy she's come across in the past. She decided to hitch her ride with you because you complement a lot of her qualities.
Your move: Keep her happy, at all time. Never try to put him down (unless, of course, you have a more pressing reason) in front of her. Show them both how confident you are with your relationship, and he will get the message.
2 She finds it easy to relax around him
Now, this is important. Could it be that she finds it easy to be herself, with him around, because she knows she needn't be at her best? When she is with you, your girl knows that she has to perform: be sexy, cool, confident... be the awesome girlfriend that you are so proud of. With him, there are no such pressures on her. Perhaps, when your best buddy is around, she considers it her "off duty" time, and therefore relaxes a bit.
Your move: It's simple: don't put that pressure on her, by reiterating what she means to you more often than what you do currently. Make her feel as "safe" as she feels with him. Rest assured: play the waiting game smartly and soon she'll realise the chinks in his armour. It is just a matter of time before she realises that he's not you.
3 May be (just may be), she's trying to impress you!
Very possible. She is perhaps putting an extra effort to make you feel nice about the fact that she rocks in your friend circle. It gives women a lot of confidence if their boyfriend's friends accept her in their fold. Her being chatty, and safely friendly, with him could also mean that she is acknowledging your taste in people you are friendly with. Come on, would you be happier if your girl is always breathing down your neck, telling you how much she hates and disapproves of your taste in people.
Your move: If you think she is taking 'advantage' of you not reacting, play it smarter, instead of confronting her. At times (very sparingly, mind you), don't advertise him so much: talk to her about some other friends and she'll know that other people too populate your world.
4 He is... actually smarter than you!
This is dangerous territory. Don't be surprised if she thinks your friend is good... very good, in fact. See, she's spent some time with you, and like it happens with most relationships, she could be getting bored of the whole set-up. And while she is in that mood, your friend would be the last guy to be around the two of you.
Your move: Expose him! For what he is, actually. Whenever you get the chance, let her realise that he is not perfect. Share some mutual story and be careful not to make him the hero. Remember, don't trash him: she must still consider him as a regular guy, not a loser.
5 She is trying to make you jealous
Most women think the key to a successful, long-lasting relationship, is to keep the guy on his tenterhooks. Don't know if it works always, but that's what conventional wisdom (for women) says. She wants you to keep working on the relationship.
Your move: Keep reminding yourself that this is a game she is playing with you. Don't fall for it. Show her that her plan is working, and play the jealous boyfriend part very smartly. Don't engage though. Most girlfriends want their guys to be jealous, possessive of them. Just stop short of confronting her/him on this and you will come across as that "understanding" boyfriend she's always wanted.