SO turning to religion

Hello ladies, I haven't been active for a while but I have a dilemma in my life. It's a long read, so I apologise in advance 😂

Me and my SO have been together for 3 years now, living together for the majority of it. We have always been very similar in or views in terms of politics, religion (both considered ourselves atheist) etc. However a few months ago my partner called me and said he had purchased a book. The book was the bible. Now he had been asking me weird questions about what happens after one dies etc for a few weeks before that (and also his sister almost dying beginning of this year probably contributed to those thoughts and questions) so I gathered he was trying to find some answers. When I got home it turned out he had been thinking about religion for a while, have talked to his parents about it extensively and ordered a crucifix necklace 😫

first I quietly nodded along, then later got upset about him not being honest and open with me. We went to church together twice and haven't been in since. He hadn't talked about it, apart from after a few drinks when he'd talk about how he's not sure what he believes in, how he's confused about religion etc.

Since he hadn't brought it up in a while I thought he had forgotten about it and moved on like with most of his interests. However, we were signing Christmas cards and he was signing them with words "god bless" which made me feel slightly odd and uncomfortable. I had a go at him earlier today for coming home too late and we started having a conversation about our expectations of one another and he said he'd like me to be more supportive of his spiritual needs. I said it's really hard for me to be supportive when he doesn't share with me what exactly his thoughts on spirituality are.

Now I have two questions:

1) how can I be supportive and stay true to my own dis(beliefs)?

2) why am I struggling so hard to accept that my SO might be religious?

Any insight or experience with something similar would be highly appreciated ❤