Sosorry, I have written my thoughts about having a sexual relationship with a separated spouse. I don't know where the thread is exactly, but if you search for it, you might find it. The subject reads something like, "Michelle, what do you think about...."
Anyway, unless you are troubled by being intimate, I think it's a great idea as long as you protect yourself from sexually transmitted diseases by using protection. I think you should have a conversation with your h about this too. But if you feel comfortable about this, being sexual leads to feeling intimate. Feeling intimate often leads to the desire to reconnect. This is especially true if sex was a problem in the past. So why give up an opportunity to be close and to trigger feelings of connection?
Again, this is strictly and individual decision and you have to feel comfortable with it yourself.
as to the rest of your situation, obviously, you can't go on forever with his coming and going as he pleases, but hopefully, this is just a passing phase. Wait and see what happens. If nothing changes, you can always set limits and offer an ultimatim. But don't do that unless you're ready to let go. Okay? Michele