Unsure. When is to soon to get married?

So my bf has recently been bringing up getting married. Like alot. He says he knows he wants to marry me and spend the rest of his life with me but i on the other had.....i have been married before at age 19 got divorced by a 20. I have 2 kids from that marriage. My bf loves my kids like they was his own he even calls them his. But we have only been together for 8 months...... Im just really scared of failing again...i love my boyfriend to the stars and back and i want to be with him for the rest of my life but idk about getting married again......i know we wouldnt get married right away but just thinking of being engaged again scares the shit out of me.....any advice girls????