Most of the time people hold feelings in because it gives them a sense of control. They're also usually afraid that the feelings will overwhelm them if they actually allow themselves to feel anything. As you've discovered, that kind of thinking is understandable but wrong. If you feel sad, angry, lonely, isolated or whatever, give yourself permission to feel it, in the moment. It will hurt, but only after you've actually recognized it and felt it can you get past it. You are strong enough - it will not overwhelm you.
Don't worry about your past or your parents or your sister - don't worry about anything but the future and the choices YOU make. Other things will only control your life if you let them. Your life, from this minute on, will be mostly what YOU decide to make it.
There are counselors and legal help available free or cheaply. Find out what is available, and take any classes you can, get counseling, and then go to court to insist on visitation.
Especially at first, your son will be confused. Do not try to convince him that he needs to choose you over his dad or your sister! That will just confuse and upset him. A person, especially a child, can never have enough people who love them, but even one person who causes chaos and arguments and hard feelings is too many! Choose some kind of nickname that he can call you - maybe Mimi? - so he doesn't have to choose which of you to call "mom." Be positive, together, helpful and adult. Remember that parents are supposed to meet the needs of their children; children are not supposed to meet the needs of adults. Think more about what HE needs than about what you need, and you will definitely be a positive part of his life.
Good luck! Post on here what progress you're making - people care.
