Hi Johnsok,
I am sorry that you are feeling this way. It is understandable to question yourself and overanalyze things after enduring so much from your relationship.
I have felt like I had BPD for a little bit. I started engaging in some BPD behaviors myself. Sometimes being surrounded by BPD for such a long time, we can pick up some of the behaviors. It is what is referred to as

. I started working on myself and those behaviors quickly dissipated. Many people here have had similar experiences.
It is understandable to have anxiety and worry about his prior infidelities and think he may currently be engaging in that type of behavior. Infidelity can be a huge breach of trust. It is normal to feel insecure, unsure, or untrusting. These are not irrational feelings.
Have you both discussed his infidelity before?