P.M.
"Stubbornness" is an adult concept. Your little guy is expressing a need in the only way he has. And not all babies are able to sleep according to the same set of principles. There are as many sleep patterns as there are babies. In spite of the fact that some sizable percentage are able to sleep through the night or on their own from an early age, there are also a sizeable number who have a greater need for contact, comfort, and bonding throughout the night.
It may not be too helpful now that it's done, but that's a huge and abrupt change to force all at once, and a four-hour cry-it-out is pretty traumatic for a baby. That's a lot of stress hormones pumping through his little body, and stress hormones (cortisol and adrenaline) make restful sleep less likely. I can't even imagine what desperate feelings accompanied that experience, but he's apparently stressed and rattled now about sleep. Tension and too much tiredness are taking a toll on him and on you.
I'm big on bonding and trust, because I've wached many, many families over my 40 adult years, and the many families I know that thoughtfully employ closeness and bonding have children who tend to be relaxed and independent from early ages. And within those families, there is a huge range of emotional aptitude and "need," even among closely-spaced siblings. So it seems undeniable that they can't possibly all fit into the same cookie-cutter pattern.
So, I were in your position, I'd be inclined to start over on the sleep separation. I would keep him in bed with me again for a couple of weeks, or at least until his sleep settled down again, and then start out by moving him into a bedside co-sleeper if it fits in your room, or his crib beside your bed, and increase the distance between us gradually.
If there's no room to do that, but you have another bed in your home, I'd trade off with mom or dad sleeping with him on alternate nights so that he begins developing some emotional flexibility while still having the closeness he finds comforting. I'd also consult older mothers in my circle, get a stack of sleep books from the library, and begin exploring other options.
At 14 months, your son won't have much if any memory of this event in a few months, though he may experience a somewhat more intense period of separation anxiety (without remembering why). But a month at his age is a *huge* fraction of his life, and the changes he's experiencing by the week are probably noticable. His sleep patterns will probably change by themselves over the next few months, even if you were to do nothing different.
So there are probably fairly small but significant steps you can make to give all of you more restful nights. I know the idea of "not going back" to a previous pattern is a big on among parents. But it's exactly that – an idea, and there's no research that suggests that it's good to stick with a new pattern that is simply not working. And I've known dozens of parents who have backed away from changes or policies that turned out to be a bad fit, and experienced only benefits from keeping a view to results, not concepts.
Good luck. Sleep is one of the most challenging areas of child rearing. And billions of children and their parents have gotten through those issues.