I was a stepmother before i was a mother myself. Krystal's bio father was married and had 2 girls before we got together. He was divorced and we'd get the girls every weekend and for weeks on end during summer break.
I felt some jealousy but not with the girls, with the x. I didn't think it was fair that I had her girls every weekend and she had hers off all the time to go have fun and party. When we had the girls, I was stuck at home with them while he went out. fair? NOT!
I did fall madly in love with those 2 girls though. They became my world and when Krystal was born, they got a bit jealous that they no longer got my undevided attention. We overcame that quickly though. I love those girls till this day. They're now both in their 20's and I do see them still. Especially now that they are aunties.
The jealousy with the x didn't last too long either. About a year before his death, his x and I were talking and getting along very well without his knowledge. We had to as something really bad had happened to the girls so we had to work together to try and help them heal from it. We've been friends ever since.
Being in a blended family isn't easy for everyone in it. Time heals everything and the feelings of jealousy does disapear after awhile.