Yes, nothing ventured nothing gained is very true. But be aware of what you have and be careful that you're not throwing that away; unless you really want to?? Complex I know, but you will forever regret not taking that first step...
You must decide what is more important to you. Your bf or this fantasy guy that you've met on here. My advice would be to meet with him for a coffee some time if he's up for it. Some times things can change just from meeting up face to face. If you both feel the same way about each other after this meeting you must then decide where you want it to go from there. But all I will say is that if you try to hide it from your bf it probably will come out at some point. So are you willing to risk the relationship you have. I wish you all the best.