Hi Wanderer.......I also married young. I "thought " I loved her but something always felt off. Like your wife , she also didn't have qualities I was looking for.
But she did have good qualities that I may have took for granted. Although at the time I was pretty messed up myself and my best qualities never shone through. I always thought that if I could only find that "right one" I would divorce my wife in a second. I never found that person that you did and it's now 40 yrs. later. To make a long story short , after almost 40 yrs. of deception on BOTH our parts , and a real painful marriage I had to leave her because I was forced to. I lost her years ago. I never really knew who I was with.
What I found out is that you have to make yourself be happy. That means with your wife or with whoever or with no one ! Things can change over time. Your wife is at least trying. Will she ever REALLY forgive you as time goes on ? Will your gf meet somebody else on line in the future and dump you ?. You said she has a child. Was she married and divorced ? If so why ? You trust somebody that would break up a marriage ? I wouldn't. That's why your suspicious.
Also you said you started drinking. What influence , if any , has that had on your life and decisions ?
Looking at this objectively I would suggest you stay with your wife . At least for awhile. Stop seeing this other woman. Follow your conscience , for now.
What did you have in common with your wife to begin with ?
Whether or not you stay with her you could be in for a world of hurt.
I know from experience.
See if she'll go to marriage counseling with you. If she agrees I think that's a good way of getting out all the things that both of you may need to discuss.
I'll say this till the day I die. Married or not you MUST always prepare yourself to one day have to learn how to be alone and be able to live with yourself. This is for sheer survival.
Don't put your life and feelings into ANYONES hands.

I wish you the best.