Giving it up

My girl T and I were having a conversation about how our once tight knit group has dissolved into a vague reminiscence of drunken nights and clammy mornings. While some friends followed their career tangents, some just simply disappeared because they now have a significant other in their lives.
Now, I am just as guilty as them -I am by no means rebuking them of their choice. However, it brings me to question- at what point does one lose their own sense of identity in order to be a part of a relationship? More importantly, why does one lose their sense of identity? It seems like being a part of a (great or ..usually...otherwise) relationship mean that you have to lose yourself, your interests, your being.
Again, I have done this myself, but in the long run it didn't work out. In fact, it made me despise him for slowly stripping me of my own. I grasp the concept of a relationship and I also understand that when you love someone- however provisional or absolute it may be- you want to spend as much time with your significant other. However, where is the balance of keeping your life- your individuality- your persona and still interconnect with your 'main squeeze'? Would you consider giving up things you once loved- the things you chose to do- as a price you have to pay in order to be in a relationship?
Part of me strongly believes that giving up your identity and your interests- giving up a part of YOU- helps a relationship deteriorate quicker than its time. Sure, there are strong urges of spending as much time as you can with your 'sweetie' and all of a sudden the temptaion of creating drunken havoc isn't as enticing as it once used to be. But, it inevitably is like being a kid in a candy shop. You want ALL you can- until you get what you asked for. And then you get sick. And you can't stand the sight of what you once thought you could never have enough of. Thats when the sweetest thing becomes sour. When the cutest gestures become irritating. When cuddly becomes clingy and loving becomes loathsome.
My personal stance- in a good relationship neither you nor your significant other would have to sacrifice yourself, but you would enhance each other in every way possible. I wouldn't have to "give up" friends or nights out with loved ones to a point where people think I've fallen off the planet. And I wouldn't have to "reconnect" with all my friends simply because I now have someone in my life. There is a difference between 'putting her/him first' and having a choice that only encompasses him/her.
I realize that when you love a person or when you accept a person into your life, you're not just accepting that person- you're accepting a whole another lifestyle. You fell for this person when s/he went out 6 nights a week or played basketball 7 days a week or played poker 5 days a month- you fell for this person when s/he had other agendas than to please you. So why try to change it? Now, I know they aren't the best example but in a way I guess Janet and JD are leading an exemplary relationship- JD went to strip clubs before he met Janet...and he still does. I guess when BOTH parties know the line- and don't cross it, you can maintain your identity and still remain the person s/he once fell in love with. And that inturn helps continue to WOW the other person everyday even 15 years down the line. ...any takes?