Am I being too suspicious

My husband is a a 55yo full-time undergraduate student and I am a 54 yo full time postgraduate student. He has recently befriended a fellow student who is twenty-five years his junior. He is bringing her over to the house at least twice a week. Each time she stays for nearly four hours . He is meeting her before classes, this morning he said he had to meet her at the gym at 9am as he thought she wasnt doing her exercises properly. Last weekend we were doing the weekly shopping. I was returning to uni this week and needed to go to a few stores to get supplies. In the first shop which happened to be the supermarket he got a phone call from her. I was told to get the shopping finished in 15 minutes. I could only do one store and had to race home only to find her at the door waiting. I had chores planned to do that day as my time is very scheduled since I returned to uni this week. She said for over four hours and I couldnt get anything done as I was expected to make her cups of tea. I confronted my husband about this and now he will only read emails and texts in a another room so I cant see who they are from. He is now always in a bad mood and each time I have to ask a question the answer is dripping with sarcasm. I just dont know how long I can stand this. This has happened once before. At that stage I was working shifts. Sometimes I would finish at 4pm and start early so I needed to get home and get things done as I had to get up early to get to work the next morning. My husband had picked up a couple of twenty year old female international students and he would meet them in the city. I would go down to where I knew they would be and by the time I got him away from them to get him home it was after 8pm. I was his mother's carer and would have to feed and settle her for the night before I could have something to eat. I just want things to go back to the way things were before this new friend came on the scene. My husband seems not to realise there is anything wrong with his behaviour and seems to think I am being unreasonable.