Needing advice on my LTR

I'll try to keep this as short as possible but if more detail is needed, just ask (or PM me). Also I do work, so give me some time to reply. Thanks in advance!HistoryI've been with my SO for about 6 years now. In the beginning (honeymoon) everything was great. Romance, cuddling, talking, etc. Shortly after moving in together we opened a business that I ran full time and he had a full time job. After a few years he went on disability/retirement from his job (many health issues). We also closed the business and I began working full time. For the past 2 years he basically did nothing but stay in bed and would rarely come out. Now he did housework some days but many were just laying on the bed, either hurting or depressed. Over these years also our sex lives have fallen to utterly nothing at all.His past is that of a partier. He lived in LA for years and did meth and did some things I blush over when he talks about it.Socially he hasn't had many friends call/text/come over for all of these years. I've seen maybe 3 friends that would come by and then not come back again for another year or two. He had told me stories of many of them that simply used him for drugs/money/roof/etc.NOTE: For 6 years neither of us have done anything more than smoke some weed and have a drink. Nothing harder and from my understanding, he didn't want to go back to this lifestyle again.Over the past few weeks tho, many of these friends have been coming back around. While I'm fine with this just for the fact that it has 'revived' him from the bedroom and gotten him moving and motivated again. I feel he is falling into a trap again. I surely don't want to be that guy that says "You can't see your friends" and I don't want to hold him back either. It really has been a polar opposite change from how he has been for many years, to the way he has been the past 2 weeks.Already we are having these people staying in our home overnight, one (being an ex boyfriend of his from 20+ years ago stayed for 3+ nights. Now he did ask after the 2nd night if it was okay that he stayed, but still.... He has stated to me that he would like to do some meth/coke/etc again, "just for fun / old times sake". He's being very sneaky about things (randomly going to get smokes which takes 10 minutes but being gone for an hour or so). These things worry me to no end.NSFW Bedroom stuff:As stated before, our sex life in the beginning was great but then diminished to nothing. Years with nothing... Now all of a sudden he comes to me and says "It's cool that during sex if I get choked out and when I wake up, your initials are carved into my body". I get the BDSM thing (it's not my kink), but WTF? Then his new 'kink' is the sub/dom thing. I think I could do this a bit but not as far as I fear he wants it to go... I've asked him how far he wants to go and all I get is a "I'm not sure".The big questionSo here I am asking you guys. Am I being too paranoid over these 'worries' that I have? Should I just let him "relive" this part of his life? We are both upper 30's - lower 40's now, is this his mid-life crisis?To me, my fear sensors are going off so strongly and my reaction is to run. But I've loved this man for 6 years. I can't imagine not having him in my life. I want this to work but I fear that it's not my decision anymore.TL;DR: SO is 40+, I'm 39, been together 6 years. Began great, life happened and things changed. Now my SO wants to do things from his past & more and I'm unsure of what to do.