After reading your question, I feel bad for your son. I understand that you would like your child to spend time with his father too. However, I would strongly suggest that you do not pay any more of your ex's bills. There are several reasons behind this.
Impact on Your Child and Finances
If you continue to pay your ex's bills, it can hurt your finances. Since you are a blue-collar worker with limited earning ability, you are already straining your finances by paying your ex's bills. Every time you help him out, there is lesser money for you and your son. Instead of paying your ex's bills, you can start college savings account for your son.
Encourages Your Ex
If you continue to pay your ex's bills, it sets the wrong precedence. You have separated from him because he is financially irresponsible. Any bailouts will encourage him to continue with his behavior. It will increase his dependency on you, and he will never learn how to be responsible. He will continue to take your advantage as he knows how to push the right buttons.
However, since you are very interested in him being part of your child's life, you can consider the following:
Have A Conversation
You should make it clear to your ex-partner that you will no longer be giving him any money. You should also make it clear that he won't get to see his son unless he gets his act together.
Find A Mediator
You should consider involving a common friend or someone from his family who would be willing to host him and your son while he is fixing his financial mess.
Several states have locations designated for child and non-custodial parent's meetings. You should contact child protective services or social services to access such a location.
Get A Child Support Order
Your state's child support department can also help you get a child support order. With this order, the funds will b directly withdrawn from your ex's paycheck. It will leave lesser money for him to waste and possibly help him become fiscally responsible. Most states have low/no-cost legal programs that can help you and your ex.
In conclusion, you are no longer responsible for your ex's finances. He needs to step up and become more responsible if he wants to continue to see his son.
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Warning: This post is neither financial, health, legal, or personal advice nor a substitute for the advice offered by a professional. These are serious matters, and the help of a professional is recommended as it can impact your future.