I need advice!!!!

My fiancé and I haven’t been doing the best the last couple of weeks. We have slowed down on the sex and have been fighting way more than we even talk. He questions me about if I’m sexually attracted to him and goes through my phone to try to find something. I love him so much and won’t do anything to ruin our relationship. We haven’t really planned for our wedding but the other day I finally went dress shopping and he asked if it was returnable. I know that doesn’t seem like that bad of a question but I have been feeling like he is looking for a way to get out of our relationship or that he will be ending things. I am really worried. Any advice on what I should do or know why he may be doing this stuff?

I have asked him why but he doesn’t give answers.