Dear Miss TB~
Both Tony and Geoff have given good advice, and if Tony's talk of a complete change sounds daunting then please consider how you are now, watching yourself make mistakes and heading where?.
You mother provided you both with the love you needed and also a role model as a parent. This is a wonderful thing and as you say you were lucky to have her.
For some reason now you are selling yourself short. You have common sense, you know what is reasonable, I'd imagine you may be attractive to others (or you would not be in a relationship) and most importantly you have all that unused love for potential children.
Add to that a relationship where you would appear to be second fiddle to a wife and kids, and do not the have the unstinting love and total commitment of a mate.
Small wonder you seek solace in drink and drugs. As I'm sure you are aware such habits only get worse, ruining body, mind and opportunities.
In your mid 30's you have time to change things around. Your dreams are not impossible at all.
I'd think you would need help. It there anyone in your life to give you support who does not think your existing lifestyle is OK?
You can find organizations to help you quite drink and drugs, our 24/7 Help Line (1300 22 4636) may be able to tell you what is available in your area.
Please don't think I other others here are being critical, we would simply like the best for you.