My DP (who I have constant ups and downs with) works with an older, very good looking, affluent and charming (divorced) contractor. He took her under his wing at work (she is retraining) and he has been good to her, but he is also clearly attracted to her. Before DP was with me, she had had relationships with older men.
Against my better judgement I agreed he could stay over in our spare room when he couldn't get an air bnb, I was unhappy about him staying and made that clear to her. He than stayed 2 nights a week for 3 weeks, until I had a massive row with DP and he stopped staying. On a couple of these occasions he was flirting with her in front of me (in my own house, when he was staying as a guest).
He sometimes (about once a month) picks her up from our house, so she doesn't need to drive and can have a drink after work. He recently looked after our son for a couple of hours, when my son was ill and she couldn't (I had already taken time off and had a meeting, otherwise I would have) - he bought my son a very nice present.
He came to our house before the office Christmas party and showered and changed before he drove her to the office Christmas party from our house. She looked more glamourous than I have seen her in years - whilst I stayed at home and looked after our 4 year old son.
She is working today and tomorrow and suggested that he stayed over at ours and had drinks. Yesterday she spent most of the day (uncharacteristically for her) tidying the house - which made me suspect it was for his benefit. I have told her I am unhappy about him coming over and we have rowed about it. Am I being unreasonable? Am I putting 2 and 2 together and making 5?