What should men do if something happens to the condom?

I (20F) was having sex with a guy (20M), and I am 99% sure that the condom was purposely removed without my knowledge. I only think this because he did NOT inform me that he was finishing at all (which was odd and unlike him). When I finally clued in and noticed that he had in fact finished inside me with no condom, he said he didn’t notice that it was off, and that it ‘must have slipped’.

Men, can you feel the difference with and without a condom? Can you tell if you are finishing inside a condom vs inside a woman? If the condom did slip, would you stop and fix it, or continue regardless?

I need input and thoughts from men, as I’m too scared to ask my guy friends and will never be able to feel for myself.

EDIT: Thanks guys, this is very validating in my frustration and feelings. To clarify, I found the condom on the bed, which to me suggested, along with his very nonchalant response, that it was purposeful.