You ex has moved on, but you're still living in his shadow.

To me, the biggest problem is that after so many years past, you're still living in your ex's shadow. You're still comparing your current situation to his, regreting having been so nice to him when he was young. I say, your son is 18 now and it's the right time to foget about your ex and move on!

Based on what you described, you are also "trying to provide your kid the BEST you can (or in fact you can't) to compensate your kid for not having a father". There are many single parents in US and they don't feel guilty by simply choosing things affordable. Even for kids with both parents in decent families, it is not uncommon (I have several friends like that) for them to make a living on themselves --- they said their parents are nice because they don't ask them to pay rents!

Anyway, don't associate bad anything with your divorce. Forget about it!