Pennine,
I wish you luck in making your decision. If you are kind but play it a bit cool, maybe that will protect you. You know, get together in a neutral location, chat, but don't make any promises or assumptions about anything. Those are just my thoughts.
I've been on the other side, only not as a sibling. Thanks to my inquiring mind, my (deceased) grandmother's half-brothers learned of her existence. I've been in touch with one half-brother. He has been pleasant and polite in his emails / letters but hasn't sent me any details about his family (not even about his father, my g-grandmother's second husband). I asked if he would be willing to send me copies of photos of his mother (my g-grandmother) at my cost but he never responded to that request. I figured, he doesn't know me from Adam, so he's playing it cool. I sent him the data I had gathered and copies of pertinent documents that prove the relationship, etc.
I've also been in touch with my grandmother's father's family. (Well, we think he was probably her father, as he was married to her mother, who seems to have left him while pregnant with my grandmother.) My grandmother's (probable) half-brother on that side doesn't want to have anything to do with me or the whole situation; I've been in touch with his son & his family and they've been very nice and open with me. My grandmother's (probable) half-sister has been very nice to me, too.
According to my mother, it's possible that my father got some other women pregnant while he was married to my mother; I wonder if I will ever hear from any half-siblings of my own? I guess time will tell...
Regards,
Josephine