Boyfriend of 4 yrs wanted to end it

My BF & I have been together for 4 years now we have a 2 year old little girl and now he just wants to end it. We were suppose to be married in sept & now idk what to do, i need help i love him alot and i dont wanna seperate household :((

Has he explained why he wants to end it ? Maybe he feels that getting married will change things ? I know a few weeks before I got married, my husband to be wanted to call it off, freaked out, but when we talked it through, it was all fine. Sit down & talk. Hope it works out :)