Am I overthinking ??

I’m not sure if I’m overthinking things or simply am acting blind , we both work at the same place and when we work together she’s home on time . However when Iam not at work she’s always late sometimes an hour or more at least twice a week . She waits until we are half way home to suddenly remember something she forgot in town and have to drop me off first . She makes appointments an hour away really early in the morning knowing I can’t get up that early and is gone literally ALL DAY till late evening. If I ask to see her phone she literally holds it hostage until she has a chance to look it over first to ensure there’s nothing I will be upset about . She will constantly complain about how broke she is and how she can’t afford the bills until I hand over all I have then suddenly she goes on a spending spree of takeout and shopping ?!?!
I had someone contact me a while back and say they saw her with someone else while I wasn’t around but I assumed this person was simply trying to start problems ... but were they really ??!
To add to matters when I first met her she lied and said she wasn’t with a man and that she wasn’t doing anything with him , that he was sleeping on the couch meanwhile I found out she slept with him and he was actually sleeping in her bed and he was still wth her ... needless to say I’m wondering if something might be going on now or am I overthinking things ??
P.s our sex life is none exsistant as in maybe once every few months ... MAYBE
please any advice will help