bad things tend to come up at the same. its the nature of things but you should do your best to distinguish between the two.
I guess you are not seeking advice here on HN on how to cope with your gf relationship - this issue (painful as it is) has nothing to do with your startup failure. So, one issue shouldnt cloud the other.
I guess that your startup failure still has value. A lot of other entrepreneurs are always keen to learn of other people's experience, so worst case your experience can turn into a blog that can lead to new followers, ideas etc..
In any case, things tend to work out in the end :) dont forget that 90% of startups fail and everyone knows that its not like you experienced something that should make you lose belief in yourself!