Hi Tywan
Yes, indeed, to finish with a girl who is pregnant is likely to cause her stress.
To imply that she has been unfaithful and that the child isn't yours would cause her stress.
Do you have any reason to think that she has been unfaithful?
Perhaps it's nerves on your part, or perhaps you have suddenly realised that you don't love this girl, after all, but this is an unfortunate time to discover this ~ especially if the baby is, indeed, yours.
Yes, a DNA test would give you proof, but to ask for one now ... well, how would that make her feel!?
You two need to have a good talk ~ but be prepared for some tears!
And yes, talk to someone else ~ a good person, whom you trust, and who is unlikely to take sides.
Good luck to you, to her, and to the baby.
Remember; babies don't ask to be born and should never be the ones to suffer.