Should I stay or leave?...

I'm a 32-year-old man in a 4.5-year relationship with a 28-year-old woman. When we first began dating, I didn't experience the “butterflies” that I had felt in previous relationships. Despite this, I chose to move forward because we share similar values, political views, interests, a mutual physical attraction, and have great chemistry in bed. On the surface, it seems promising, right? Now we're at a pivotal point—it's either time to get married and start a family or break up and begin anew. She is deeply in love with me and experienced those butterflies from the very beginning. In many ways, she is the ideal partner—loving, nurturing, would be an excellent mother, and is financially stable. We have much in common, including a passion for psychology, visiting museums, and enjoying nature. Both of us desire families and children. However, I find myself grappling with doubts about whether she is truly the right match for me. I've grown fond of her and cherish the time we spend together when work isn't wearing me out. I feel stuck at a crossroads. I never envisioned being my age and contemplating starting over. The thought of becoming an older dad is daunting if I choose to begin again now. While I love and care for her deeply, and she would undoubtedly make a wonderful mother, I can't shake the concern about the absence of those initial butterflies. I'm anxious that this lack of excitement might lead to problems in the future.