I think if you really only want an online relationship and itīs clear from the onset that it will stay thus, you can always make an agreement with the dom to keep your identity as hidden as possible.. use a mailadress that does not give a name and that you use only for this, if you share pictures or do cam... decide for yourself if you are comfortable with showing everything or if it would be better to wear a mask...worst that can happen: you invest a lot of time and feelings and he gets nasty, your heart may be broken, you may feel bad but you just have to shut down the mailaccount/ messenger account you used with him and are free of him. If you realize a year or more into the relationship that you feel safe enough to reveal more.. you are a lot safer because most trolls donīt invest as much time and to constantly pretend to be someone else (personalitywise) over such an extended time is almost impossible as one will inevitably contradict oneself. If he comes around in the scene you could even ask if he would give you r/l references if he trusts you more than you are at the moment able to trust him, people also on the library who have actually met him.
If you feel a connection with one person tell him how you feel, take it slow but donīt be afraid to live because of a bad experience. Be overcautious, take babysteps, back of if you get any little feeling of wrongness but donīt let your black sheep rob you of the chance to make better experiences. Thats the moment he really wins
Yes, there is always the possibility of heartbreak and always the possibility to find, once again, a black sheep but sometimes you just have to dare a something to win the something.

That just wanted to get out ;-)
Deigja