I would not be doing you a justice if I wasn’t brutally honest to you. I think – from what you’ve said – he is using.
Firstly, stop blaming yourself. For wanting to see the good in him, for trusting him, even for tolerating his use and staying with him.. STOP BLAMING YOURSELF. You are a good, loving person – and that is NOT something to blame yourself for. Not trusting him, that is NOT your fault. He is given you reason to not trust him anymore. Two people make a relationship and when one person breaks that trust, it is THEIR fault. It is not your fault, or your problem to just get over it and rebuild it.
I think the best advice I would give you, is to start putting in place practical things to protect yourself – as he is at home with you. Because if.. IF he is using, it is only a matter of time before things will start going missing from your home, as he looked to fund an increasingly bad habit.
Don’t expect honesty from him. You won’t get it. You need to start thinking of him in these terms.. yes there was a loving caring guy.. but if he is using and has not been clean for a substantial amount of time.. then you are living with Mr Hyde.
Can you speak to him? Is he dismissive? How would he react if you asked him to take a drug test? If you openly tell him you are finding it difficult to trust him.. and want to rebuild the trust.. (a person with nothing to hide will not object as violently and vehemently as a user). If he loves you and genuinely is clean, then this should not be an issue.
My partner offered to take a test (knowing the recovery centre are not doing them right now). Approx 7 days later, after I found his drug contacts on his new phone.. he emailed me and admitted to the ‘occasional lapse.’ He looked me in the eye and lied when asked ‘are you using’? He told me he’d kicked the hard stuff and was only smoking weed. Know this.. an addict will lie and lie and lie. Never forget that.