Every person in the world either has a friend who has had a significant other at some point in their life, or at the very least knows someone who fits in this category. Since this is the case, then most everyone has experienced (whether first or secondhand), the 'pulling away from friends' that happens with a first relationship. A term has not yet been coined for this phenomenon, but it is something that is very real and that happens to most of the population. Some would argue that it is more the case with women, which may very well be true, but it is also common with men. A reason that it might resound more with the female sex is that women tend to talk more often and to share more information than men do, and when there is a change in the level of their communication, is could very well be more obvious.
Regardless of whether a person is male or female, if you have a close friend and have therefore experienced this change firsthand, it can be very hurtful. Friends can easily be lost in these situations, so treading carefully is recommended. If you have a friend that is going through this, it is important to rememebr that it is hard on both you and your friend. While the well-meaning friend may see this situation as the person who is newly coupled up caring only about his or her significant other, this is almost never the case. Making sure that you (the 'injured party') realize that your friend is not doing this on purpose will eliminate a lot of the possible strife immediately.
When a person is in their first relationship, they will almost always spend a large amount of time with that person. The simple reason for this could be explained as that person just does not know how to be in a relationship. It is anyone's guess what type of romantic relationships they may have observed prior to starting their own, so they often do not realize what the appropriate amount of time to be alloted to their significant other should equal.
Almost always, once a person has gotten over the 'first relationship' hump, they will know more about what is socially acceptable concerning spending time with their significant other. As they continue to date and to have new and different types of relationships, they will eventually figure out that dating someone new does not mean spending zero time with your friends. When it comes to figuring out this equation, balance is key. It is important to spend enough time with friends so that they do not get upset and so that they remain good friends, as they will last longer than most relationships. By the same token, each romantic relationship that a person is in has the potential to be the most lasting friendship of their life. Therefore, each and every romantic relationship should be evaluated to make sure that enough time is being spent both with the significant other and with friends in order to keep everyone happy. If friends are saying that they are being neglected, this is probably the case.
So remember that friends will generally have your best interests at heart, and it is good to listen to their advice with relationships and all other bumps in the road of life. Make sure to value them, and to tell them how much they are cared for. Think twice before tossing them away for a new relationship, as they are the ones who will be there for you for the long haul, if you'll only let them.