Bristol Palin just told TMZ she is "heartbroken" in the wake of her split with her baby daddy Levi Johnston ... explaining, "I so much wanted [him] to be a real part of Tripp's life."
Bristol added, "I was really convinced Levi was ready for this. I was wrong."
As we previously reported, Bristol secretly dumped Levi three weeks ago after she claims Levi told her that he may have fathered a child with an ex-girlfriend who is currently pregnant ... and then lied about shooting a music video in Los Angeles.
Bristol tells us, "He told me -- he told everyone -- he wanted 'out of the limelight' and was ready to settle down."
Levi claims the whole thing is a "misunderstanding" -- and is adamant that he is not the father of his ex-GF's unborn baby.