@1confusedguy,
Thirteen year olds are confused and confusing at the very best of times.
Thirteen year olds whose parents are in an on-off relationship - oy.
Thirteen year olds whose parents have split and starting new relationships - double oy.
I really think you need to focus on getting your relationship with your daughter straightened out.
If your ex is the custodial parent, let her sort out discipline etc. As the custodial parent, she needs to be responsible for that. I'm not suggesting you let your daughter get away with bad things, but your ex needs to step up on that. You can back her up on disciplinary decisions but try not to take the lead. It doesn't read as if the current situation is working for any of the three of you.
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Does your girlfriend have a timeline for starting a family with you? Are you in a financial/emotional place for starting a new family?