It sounds like this friendship has run its course, which is not unusual with former co-workers. When we're employed at the same place, we have an endless number of things in common: gossiping about other employees, complaining about the boss, discussing projects, and sharing our day-to-day lives. When we no longer work together, that closeness can come to a screeching halt.
While some people today are satisfied with friendships that exist exclusively through texts, e-mails, and social media posts, it sounds like you're not one of them. I'm not either. If someone doesn't take the time and make the effort to interact with me in person, I end that friendship.
While some folks brag about 3,000 so-called friends on Facebook, I hold the designation “friend” in much higher esteem. I can count my true friends on one hand. To me, a friend is someone who took an hour-long walk with me after my son got diagnosed with autistic. A friend is someone who came to my house after the holidays so we could plan our health and fitness routines for the new year. A friend is someone who wanted to sit with me and listen, watching my facial expressions, body language, and hand gestures when I discussed the problems I was facing in my marriage.
While it's always hard to end a friendship, it can also be liberating. It allows us to open up to meeting new people. It can be empowering to let go of those folks who, in their never-ending busyness, make us feel insignificant
The author, Scott Berkun, writes this about folks who are always so occupied with other things, claiming that they don't have time for us:
"The phrase 'I don’t have time for' should never be said. We all get the same amount of time every day. If you can’t do something it’s not about the quantity of time. It’s really about how important the task is to you. I’m sure if you were having a heart attack, you’d magically find time to go to the hospital. That time would come from something else you’d planned to do but now seems less important. This is how time works all the time. What people really mean when they say 'I don’t have time' is this thing is not important enough to earn my time. It’s a polite way to tell people they’re not worth your time."
Friendships come and go and that's just a normal, natural part of life even though it's sad. I wish you well.