Unsure what to do

I’ve been dating my girlfriend for a short time and some things are really bothering me. Early on she told me about a past situation where she was involved with someone who was older and already in a relationship and carried it on only stopping due to the guy moving away, and she didn’t seem to feel much remorse about it.

Since we started dating, I’ve also noticed some inconsistencies like saying she’s too tired or sore to do things with me but then doing them with other male friends and reaching out to an ex out of the blue “to clear guilt.”

I really like her, but these things are messing with my head and making it hard to feel secure or trusting. Am I overreacting, or are these reasonable red flags? How should I handle this?