Friendships change big time when THIS happens...
In a way, this is to be expected. People get busier and tend to put their significant before anyone else. And once kids come along, this is only magnified tenfold.
The most noticeable shift is that face time with the friend becomes very hard to come by. In most cases, the friends still manage keep in touch via text, email, or Facebook, but plans made with partners now preclude outings to the movies, concerts, and elsewhere that the friends used to make at the drop of the hat.
That's not to say that seeing each other becomes impossible once one or both friends are in a relationship, but it takes more effort and planning. Obviously, any proposed plans with friends now have to be run by the significant other, who may or may not be on board. That was never an issue when the friends were both single.
A great example of this is my friendship with an ex co-worker of mine, Elizabeth. During the two years we worked together (2009-2011), she joined me on several outings with my wife (who was my girlfriend at the time) and closest male friends. About six months after I left the company, she hooked up with a guy she'd supposedly known for several years. Let's just say she moved at blazing speed: she married him a little over a year later and is expecting her second child with him in October.
Our friendship hasn't been the same since I left the company. That, coupled with her new relationship, made it a foregone conclusion that going forward we'd only see each other at weddings, baby showers, funerals, and other special occasions. Spur-of-the-moment get-togethers at restaurants and the mall? Those are a thing of the past.
In a way, I miss the friendship we used to have. (She's also been the best coworker I've ever had -- no one at my current company even comes close). But I understand that, like life itself, friendships evolve. Going from a single gal to a married mother of two changes one's life in a big way, and it wouldn't be fair to have the same expectations of the friendship as I did five years ago.
Even when I do get to see her in person, it's not the same in that now her husband, who has a very flamboyant personality, accompanies her everywhere. I feel like I have to hold back a little, whereas before I would joke around freely. What's more, having kids in tow changes things quite a bit.
I'd like to think that her inviting me to her bridal shower, wedding, and both baby showers signals that she still holds me in high regard. She doesn't have to invite me to these events, but it seems my presence means enough to her to extend an invitation.
I'm cognizant of the fact that many friendships don't survive distance and sweeping life changes, but luckily, ours has. There's a "season" for some friendships beyond which it begins to fizzle out.
As long as both friends can adapt to such changes, there's no reason it can't last for the long-term. However, in order for that to happen, both people have to put in the time and effort. A one-sided friendship, sooner or later, will go up in flames.