Is My Partner Cheating On Me With His Ex Wife?

My partner and I have been together for 17 years. We have no children together. Our children from previous relationships are adults with families of their own. My partner was divorced from his wife 10 years before we met. She has since remarried 3 times and her last marriage (4th) has just ended. They had the usual amount of contact when the children were young, but not so much since they became adults as there was no need. Since last August (I think this is when she started to become disillusioned about her 4th marriage) she has been regularly contacting my partner with her problems. Even telling him that he was the only one of her 4 husbands that she really loved. I think this revelation from her has totally gone to his head - this is a woman who he never had a good word to say about, she ran up a £3,000 debt on her son's credit card and refused to pay it. She had an affair when they were married and ended up marrying the guy she had the affair with and having 3 more children, she then had an affair on him and married her 3rd husband with whom she had another child (6 kids in total). Over the last few months my partner has been running around after her and her kids (the ones that are not his) giving them lifts, fixing her car, giving them tobacco, paying for them to have meals out and all sorts. I have only found this out from reading their text conversations - I know I shouldn't but when you are living in a permanent state of anxiety because you know something is going on you can be lead to act out of character. More recently I have found that he is deleting their text conversations, he isn't open with me about what he is doing for her, in fact he hardly ever mentions her anymore, which is strange because he would have been the first to have a laugh at her 4th marriage breaking down, but he hasn't even told me about this. Obviously the road is clear for him now she is single. What hurts so much is obviously I cannot trust him, what does he have to hide that he deletes their text conversations (I know this because the test messages are still recorded in his call log and he is not tech savvy enough to realise he needs to delete these also. Obviously the call log does not show the content of the conversation). What also hurts is that whilst he is doing so much for her and her kids, he does absolutely nothing for me. I work full time and have to manage all the housework, decorating, gardening and repairs which I also have pay for. He does nothing around the house, doesn't so much as empty his own dirty ashtray. I literally feel like a single Mum who has the responsibility and another person to look after. He never tells me I look nice, never arranges to take me out. He looks forwards to the weekends - not so that we can spend more time together, but so that he can go out on his motorbike and visit several of his mates and possibly his ex wife. Am I paranoid or am I a dumb ass? Am I seeing way too much into this? He is hard to talk to the minute I try to raise an issue he becomes so defensive and make out like it is all in my mind. Any advice please. I feel like I am going out my head.