Tricky situation. You have to do what you want. Don't let anyone pressure you either way.
For the record i'm not telling my Mum, she deserted my sister and I when we were little(11 me, 8 my sister) and our dad brought us up. I have seen her on odd occasions, usually family funerals as i still saw my grandparents.
However i don't believe she has earned the right to know what i do in my life as she hasn't expressed any interest in the past. She will probably find out through other members of her family that i am still in contact with, but that's up to them if they want to tell her. She won't have anything to do with my child. But that's just me. You need to do what you think's best.
xx

im in a similar situation with my real dad i wanted him to no but no1 else wnted me to tell him, i decided that i didnt want him involved in any way so it would be cruel to tell him then to say but aint ever havin anything do with it. neways u just gotta follow ure heart and just do whats right 4 both u ure baby and ure oh