On a long road trip with my bf and registered domestic partner (37m) in his truck, I (32f) dropped something between my seat and the center console. When I reached down to grab it, it couldn’t feel it and so I felt around and I found a lipstick. I do not wear lipstick and did not recognize this as something I’ve ever bought which was weird because I assumed it was my daughters (12) who loves lip gloss etc. I mentioned it to my bf and threw it in my bag to give back to my daughter. He acted annoyed like it would ruin his truck as he likes to act like my kids are going to ruin everything he owns and then asked if I threw it away so it wouldn’t ruin his truck. (How tf a closed lipstick is ruining anything idk but anyway) I said yes even though I threw it in my bag and I felt like his reaction was off and was weird he insisted I “throw it away”. The next day after getting home, I gave it to my daughter and said “I found this of yours” she said word for word “this isn’t mine. I HAVE NEVER SEEN THIS IN MY LIFE” such choice words but ok. My bf was right there and I didn’t want to make a big deal so I just moved on and was going to throw it away but it was bothering me so I looked at it and it was almost all used. Like not something my daughter could have gotten and then lost and forgotten she’d had it and like I said I know I’ve never bought lipstick like this. I asked my sister what to do and she said just ask him gently about it making clear that I’m not accusing him of anything. I did that and he blew up at me. Stormed off and then yelled at me and said I’m accusing him of something even though I noted that I had expressly said I wasn’t trying to accuse and was simply bothered and wanted to talk about it. I feel like his reaction is a red flag which I also stated and he said that maybe if I leave he can never have anything left in his truck again by me or the kids which I feel was pretty low. This is probably the biggest fight we’ve ever had but the past few months I’ve been feeling really anxious like he’s hiding something and this just tops that off. Am I overreacting? Should I apologize or should I just move out? We’ve been together 3.5 years and he’s been an amazing step dad to my kids but I just feel like he’s hiding something even if he’s not cheating and he’s totally defensive and unapproachable if I mention ever being anxious about it.