@Nicole2726,
Congrats. You have awareness about what is bugging you. Some people don't have that gotten that far..as they aren't introspective.
FYI, you have two of the best advisers contributing their caring helpful advice. Good for you. See that? You exude a sincere quality that make even people on the Internet like you.
Being in management can be a whole other sort of environment. When you are with other managers, they might feel competitive..or the atmosphere at work is not one that allows closeness with colleagues. Being friends with people are below management might not be a workable goal. Having civil or cordial relationships there might be a more workable goal. That might depend on the work environment and corporate pressures and history.
Suggestions
Here's a possible interpretation and some suggestions. You have some pretty good stuff going on already in your life. You have less friends than you like and clearly that is a concern for you, but have you thought that maybe you have a few good quality friends a situation that many would envy... and you have a b/f
As for the talking-over and assertiveness things...well, that can be overcome. There are some good assertiveness training classes that can help steer you towards a different way of assertiveness - one that is more effective because the way you might come across might be working. I went through as good class and it helped me a lot.
the talking over thing I too have experienced all of my life to some degree...less so now. It was a learned talking style in my family. I had to dial that way back for me at work and with friends circle. Eventually I then learned a new way to avoid reacting to it when other people did it to me. Often times, it's just an awareness issue.
Though, if it happens repeatedly, if they're your friends and continue doing it, you may have to reconsider being around them. A good faith effort should be made to let them know (w/o accusation or blame game) how when they talk over you, how you feel. That can take some time and working with that..in maybe an assertiveness class or counseling.
This can work...but not always. Then it can be time to find a different friend. This all takes time.
In the meanwhile, I would find some hobbies...and activities that interest you, that may or may not involved others. MeetUp is a good resource for interest groups...that people get together in your local area and share their love of dogs, walking, tennis, writing, photography..you name it.
I hope this helps.