Are you in treatment for your BPD, Meds of course don't do much of anything for Borderline , but DBT is good.

As for this fellow. I would just back away, People meet and chat for days weeks and months online and may never know who that other person really is. That's just the reality.

Work on building your self esteem and calming the bpd and then actually look for a relationship , sure you can start just chatting , but someone you can actually met in person and spend face time with.

good luck