How do I (F31) understand my boyfriends (M31) change in sex life?

We have been together for four years, and our sex life has really changed. I understand this happens in long term relationships, and I know it can slow down, and life can sometimes just be "not sexy" and so its not always a priority.

I have had a number of conversations with my partner about our sex life, as although I understand it chanages, I don't want it to disappear. For me it is an important part of a relationship, or at least assist in important needs for me, which are feeling wanted, feeling attractive, and feeling emotional connection.

Our sex life has not only slowed to very little, its also changed to very minimal when it does happen, and I'm finding it difficult to even enjoy when it does happen. We used to explore with toys, fantasies, talk to each other etc. Now, if it happens, its a roll over, a tiny bit of fore play, then go and done.

I have talked to him a lot about this, and in someways hes listened and is trying to meet my needs in other ways, and has tried to engage in our sex life a bit more I.E. doing some of the flirting we used to, mentioning it before me as I was feeling like the constant initiator.

I don't want to complain when I feel like he is trying, I understand things take time and it can be a work in progress, but also, I still feel a lack of connection when we're actually having sex.

I also want to understand more about whats changed for him. Because I don't fully understand, I've started to feel really insecure around our sex life. I'm anxious about initiating, I'm over thinking when its mentioned then anxious when it doesnt happen I've done something wrong etc. And, naturally, it just feels like a constant blow to my self confidence. I'm trying really hard not to let it, but when I don't understand why, my mind naturally goes to make it make sense by exploiting my insecurities.

Yes, I've considered the cheating option. I don't think he's cheating, honestly I dont know where he would have the time. But what bothers me is my lack of understanding makes me worry this, and I just don't want to feel that way. I want to understand, and I don't know how to approach it with him without making it about him doing something wrong, and actually get a good conversation that helps us move forward.

So far his reasons have been life changes/not having the time, and that relationships naturally change overtime. Although I understand this, I don't feel it fully explains his drastic change in wants in the bedroom.

Am I over thinking? How can I ask for my needs without putting pressure on our relationship? How do I understand his needs/wants when he isn't the best at explaining his feelings?