Should I let my son spend the night at his dad's

My son's father left me when I was pregnant. He was on meth and just doing a shit ton of bad stuff. He came around over a year ago and said he wanted to see his son and he was clean and I said no because I didn't trust him and he said he would take me to court. And he did. He got supervised visitation rights every other weekend. It wasn't really that bad. He came by they talked, played video games together, stuff like that. Every other weekend turned into every weekend with time. He calls and checks up on him. Got him gifts for his birthday and Christmas, they seemed to be developing a good relationship. He got a job so thats good. If he ever can't see him that weekend for some reason he will usually do what he can to make it up. It's been okay coparenting. Our son is 15 and I'm happy he's building a relationship with his father. Its been over a year now and he recently asked if our son could spend the weekend at his apartment. I'm not really sure how I feel about that. The most he's spent alone with his dad is maybe 7 hours whenever they went out to do something together. Also I'm starting to wonder if his dad is gonna try to go for 50-50 custody if I start letting him spend the night and I just don't know how I feel. I don't think my ex is a bad guy and I'm glad they have manage to build a relationship, but as for spending the weekend I just feel a little uneasy... What do you guys think?