Which two words were combined to the contraction 'haven't'?

Have not

Explanation:

Have not combines to become haven't. For example, I have not ate food today you can also say I haven't ate food today.

Have and not

Explanation:

Haven't to Have, not is just taking the O out

in june, we will have been married for eighteen months. (i am assuming this is what you want? the sentence, as you have presented it, is grammatically incorrect--   you want it corrected, yes? )