Sabby's advice ⤵
I think you should put whatever you have with B on pause until you figure things out with your ex. Maybe you can end up having something really special with B, and you probably won't get that if you are still going after the same person over and over again. I think that not only you have to clear things up with A but you have to also clear things up with yourself. You can't keep being in an on and off relationship with someone forever. Some things are not meant to be, and maybe this is one of them, regardless of your feelings for her. I think that if you keep being indecisive, you will end up putting both of your relationships at risk, and maybe you might hurt them, too. You need to make a choice: who do you get along with most? what are the advantages of each relationship? what are the disadvantages? Think about it, clear things up with your ex and figure the rest out from there. I hope this helped.

 Leo's advice ⤵
I think you should be done with your ex before you go on with the Online girl. You're probably still going back to your ex because she's physically there whenever you want to see her whereas the online girl is no where near you, so you might want to wait until you can actually be in a committed long distance relationship. So if you feel like you have a strong connection with the online girl, you might want to let her know that you can't do long distance at the moment then figure everything out with your ex, whom you seem to not want to get away from even though there's a slight chance you're only going back because she's just there, you know? But whatever final decision you make, make sure you are only focused on ONE girl and not leading the other one on. Hope this helped.
 

Lime's advice ⤵
Before giving you an advice for your feelings, I'd like you to think about these questions to yourself: What is the reason for your breakup with your ex, and what keeps pulling you back to her side? Have you met the other girl face to face yet? Instead of seeing her online-persona, are you sure she's the type you'd like to start a relationship with? I also agree with the other counsellors on the part where you should figure out your heart with your ex first before pulling in someone else into your love life. You must decide clearly about whether you're leaving your ex for good, or you want to start a brand new relationship with someone new; unless you figure this out, you'll be harming both yourself and the two girls from your indecisive behaviour of going back and forth.