I think LW needs some therapy for her obsession with kids being what creates a bond between people. That isn't really what's going on for them; the child existed before this relationship, and maybe (just maybe) there's some innocent misunderstanding going on re: the DNA test.

(DNA tests can be wrong, sorry Amy. Cross-contamination, labelling mistakes, insufficient DNA, DNA too degraded for whatever reason by the time the test is actually done... and someone lying/providing the wrong DNA sample deliberately/etc.)

The guy may have lied, but the LW doesn't actually say so. She doesn't explain the situation there at all.

So we could also have a situation where a mistake was made or the liar was not LW's boyfriend, and she just refuses to forgive him for having a child with someone else before meeting her. What?!