"An escape artist in my own mind" - what a great phrase, and how well it sums up the lessons that some of us learn through long association with an alcoholic! That was definitely my state of my mind during the later years of my marriage (and contributed to why email approaches from my own version of fantasy dude seemed so positive and affirming at the time - here were all the ingredients of a great escape to fantasize about!). My other "escapes" included reading all the time and getting involved with any volunteer cause that would have me - none carried the same risk of sleaziness as carrying on an online flirtation/liaison with someone I wasn't married to, but all served the same function, I realize now in hindsight.
Your current relationship with your real-life partner may be affected by this escape-artist conditioning. If you recognize it for what it is and deal with it appropriately (telling fantasy dude that you think it's better not to be in contact), taking these actions might be part of your healing from alcoholism.
Your current relationship with your boyfriend sounds really good. You know the difficulties that may lie ahead (his daughter hitting adolescence with a bang), and it sounds like you have a realistic handle on how to appreciate the good qualities in someone while also acknowledging that they have other qualities which irk you. I suspect that if you say "so long and good luck" to fantasy dude, you may sense a feeling of peace creeping in (although your initial emotional response to closing off this source of validation may be frustration or ambivalence).