To have or not to have? (2nd child)

I’m 42, wife 39. We want to have a second child so that our first (3 1/2 years old) can have a sibling growing up. I’m ok with the extra effort and energy of taking care a second child but what I can’t handle is my wife’s emotional turmoil that potentially will happen. Sometimes when I see her handle the first, she gets upset and emotional and sometimes affects the child and me. It’s gets me really emotional too and it take a lot of effort to calm myself from extreme suicidal thoughts and separating to been grateful to her. She still very insistent to try for second one (via IVF for us) but a part of me is afraid that it will affect our me and eventually the marriage. People with more than 1 child, does it get worse? Should we go for it and hope for the best? Honestly I can live with just having 1 child.. but thinking for the child….