C.O.
Okay Lesley - you want be set straight?
How much do YOU invest in the relationship with L?!
How much do YOU listen to HER?
just because you've been friends since 6 or 7 doesn't give you ANY "hold" on her.... you have to INVEST in your relationships and not the be the one always TAKING from it. You state she's a busy-body - however, I can tell you that it tells me she is TRYING to take an active interest in your life - but you blow her off....if I was her, I'd seek friendship elsewhere.
You are frustrated because all of her attention is NOT focused on YOU and ONLY YOU....you can't claim her as a friend if all you do is suck and take from it - you need to give back...
What's wrong with her developing a relationship with your SIL?! It's obvious that your SIL GIVES BACK in the relationship so of course, L will be more inclined to seek a friendship where she is getting something in return.
MAYBE your BIL & SIL don't invite you to their home because you take too much from them as well...I know this sounds mean and I want you to know I am NOT trying to be mean. I know that I do NOT want to be friends with someone who doesn't "give" back - not material things but TIME, LAUGHTER and one-way phone calls.
It could be that YOU are being seen as the person that sucks the life out of the room - by wanting to be the center of attention or doing all of the talking and in doing so - people CHOOSE to look elsewhere for companionship and friendship....
Why not try treating your SIL and L the same way YOU want to be treated? Let them talk some in a conversation....do things with THEM on THEIR terms and THEIR turf....
Step outside your box. View yourself as others might see you...you might not like what you see but it's NEVER too late to change it.
GOOD LUCK!