Hopefully you have managed to find some resources, online or in print form, to make you feel less alone and offer more perspectives. But those will not always be helpful, especially if you are dealing with specific problems. From time to time, we all need to just get things off our chest and feel heard. This is why your social network is your safety net.
Now I know that you are going to say that it is easier to say than to do. And yes, finding good people to bring into your life is not a simple task, but it is not impossible either. You can start with online groups and forums on polyamory. See if there are any meetings in your area for people in alternative types of relationships. Even if there are not, being active in online groups can help you make connections with others who might also look for a friend.
If poly people are hard to find in your area, that does not mean that you can’t connect to other folks who are open minded. Take up a hobby, go to a group of any sort, try to reach out to others. Being open and honest is usually a good way to attract the right kind of people around you.
Even if you are an introvert, having a strong network of friendship and support is important. Think of it as an investment you make in your emotional well-being. Besides, the more people you have around you, the more people you can rely on to give you advice and be there for you. It also removes the very dangerous temptation of complaining to one partner about another partner. Not to mention that you get to spread out the misery, in order to not burden just one person with all your problems, while giving you lots of humans to share your achievements with.
So do not hesitate to reach out to others. Once you make a purpose out of it, you will see how many folks are willing to go out for a coffee and share random stories or memes with you. Give it a try!