Brief Answer:
Likely anal problem but not serious. Needs work up

Detailed Answer:
Thank you for asking

I read your question and i understand your concern. Blood stained undergarments suspicion or anal area location should always be evaluated for the likely pathology like anal fissures, hemorrhoids etc and should be given benefit of the doubt before labeling them a cheat . With any history of straining or constipation the possibility of the above mentioned pathologies increase further.

Get your partner evaluated for a digital rectal exam, a doctor will have a naked eye examination of the anus and will do the rectal exam to sort out any pathology for the blood and we all will have our answers.

I hope it helps. Take good care of yourself and your partner and dont forget to close the discussion please.

regards
Khan

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