How to choose ?

Sorry about my ranting this morning but it's been on my mind heavy! My s/o has a baby from previous and I hate that he does in every way because I always wanted my first to be his first. We had a miscarriage and since then I can't seem to fall pregnant which makes me even more upset because the one thing I want another woman has and takes for granted! Which makes my thoughts wonder.... My ex comes home in 3 years I was thinking what if I didn't get pregnant until then and some how things didn't go as planned and me and my current s/o didn't last , and I get pregnant by my ex... That would be some weird shit, are these signs In disguise ? but all I want is a happy family it's driving me nuts !!