I think it may well be a natural biological urge, those can be quite strong, even when we know we are not in a good position to parent.

I remember feeling like this when I wanted another baby after our family was complete, I knew the logical reasons why it wasn't a good idea but I still had a strong maternal urge so I 'get' this.

I just had to ride it out, one of the ways I coped with it was to spend time with others young children, I even did childminding for a while, that reminded me how much unrelenting hard work they are but satisfied my need to nurture. Maybe if you could spend time with your cousins and help out with the babies that might help sate some of those urges and also be a good help to them and strengthen your friendships.

Sorry I can't be more helpful - biological urges can be strong and quite a challenge.