Resentment is Surfacing

I love my SO more than I have loved any other man enough to finally want to have another baby in my 40's. We have gone through lots of ups and downs in our relationship throughout the years but always find our desire to want to be together and with no one else. A year ago we decided that we both wanted a baby together. You see, we are both single parents with one child each both 14 year old boys. I never wanted to have another child up until my SO and I actually discussed it. I was full of joy and the desire to conceive was instant! After a year TTC we find out he had issues and had to take meds to help us in TTC. Our relationship is feeling the stress, our sex life is suffering and I am trying to stay positive. He has become very insecure in our relationship and it drives me crazy. I feel that I am starting to resment him