I'm going to assume that with a four year reltionship and a kid you can talk about stuff in the open. If that is correct, you should directly (not aggressively) ask what you're doing or not doing that is making him look for a back up plan (since that's what he's doing). From there you could try to negotiate (not attack eachother with situations and habits), decide to call it quits, or if it doesn't bother you, change what he wants you to change. The last one is ineresting since it depends on how reasonable the request is. He simply might just not be your soul mate, chemically compatible, whatever term people want to use. He might be worse (someone who uses you). You need to weigh those possibilities when you hear his requests. He might also be looking for a back up plan which is what it looks like to me. If it turns out it won't work, don't try to prolong an inevitable break up, it will only hurt you both more. If your attached to someone who doesn't love you, than you should break up and gain some bearing over your mind before trying it again. Nothing wrong with your mind, it just needs to settle out the drama from the reality.
I've been in all three predicaments I defined above.