3.5 years of relationship, told families about each other, but suddenly bf feels he wants to “explore” before committing for marriage! Im 28F he is 30M!

I am breaking apart! All of this came very suddenly! I was his first sex, first gf, first everything. We were a happy couple, everything perfect. He told his family about me as well, and they liked me. My family liked him! But suddenly he started acting like he didnt want a marriage anytime soon! I further probed him and he realizes that if he stays with me he will always wonder if there is another woman who he might be more compatible with.

This has shaken my world! All of this is so sudden! I had no idea he was thinking about these things! He is a totally different person to me now suddenly! I cant fucking deal with this I am breaking apart! I am in shock and I cant process this thanks