First some shorthand, so hopefully you'll see the links, or lack of links more clearly.
1 = primary emotional response
2 = secondary emotional response (also known as obsession).
1a = image attached to 1
2b = Beliefs attached to 2
-> = leading to, attached to or causing
1 is the underlying cause of 2. (1 ->2) Dealing directly with 2 e.g. the thoughts associated with 2 is a great way to keep yourself maintained a bit, but does not deal with 1 which causes 2 so the problem can resurface. 2 is hiding 1. And 2 hides 1 in such a manner it is difficult to get at. But you can get in around the edges when you see the construction of the beast. I recommend writing out a model for yourself if models (flow chart etc) work for you.
Here's how it is built.
1 -> 1a < -> thoughts about 1 & 1a -> 2b <-> 2.
As you can see, 1 is far removed from 2, though going from 1 - 2 can be instant.
1 is a subconscious effort to prevent something terrible happening. Something triggers the subconscious which reacts to protect you. The subconscious uses what it can (worldview, information, experiences) to create 1a - an image of what originally triggered the emotional response. 1a is typically composed of past problems, failures, experiences that were really horrible - as a mechanism to induce fear it works, and some may recognise what is unresolved and why they got triggered, and some (like me) may runneth screaming "Fuck that shit, it hurts too much". This (resolution or run) is the "thoughts about 1 and 1a" process following 1 and 1a. The image can be instant, take you completely off gaurd, and so we may react instead of catch it for what it is (past shit, unlearned lesson, unresolved trauma, crooked worldview, whatever it is).
The thought of my losing M causes 1. FEAR. Fear of not being able to handle it. Fear I will hurt (physically &/or emotionally) M or someone else or myself. Fear I will become a complete wreck. I've hit a man who was with 'my' girl before and felt so bad about it, I've been a blithering mess before, my subconscious knows this and is trying to protect me. It uses the most powerful images it can find to try and protect me - doh. The fear I can't handle it has a process too. If i don't handle it -> I'm not good enough -> then I wont be loved. We just want to be loved.
It's not just about fears here though. There's a lesson to learn. For me... It's about forgiving myself for mistakes in the past, about me doing a better job of looking after myself today, about me dealing with my jealousy, about me enjoying my own company. It's not about being loved by others, it's about loving myself. I want to be loved - love myself! M is not in this picture, I got to take my power back, which is where this can actually help things with M. The images of me at my worst combined with thoughts of worst case scenarios are a powerful combo that spell out doom and gloom. I MUST do something to fix this, so I make a dickhead of myself and run to 2b
Opting to run, and fueled by scary thoughts about 1 and 1a we go into avoidance mode 2b -> 2. 2b is the beliefs - I can control (handle) it, if I pay enough attention I will resolve this issue and never go to 1 again. I go over and over what is potentially wrong, and how I can fix it. This, as you'd recognise, is 2. OBSESSION!
I can fix it, I can handle it, how do I, what if I, what if she.... then 1 and 1a pop in and I recoil in fright back to 2b - I can control, I must control...
See that horrible 1a, telling me not only if I get dumped will I be alone, I will lose it, grow dishevelled, lash out, be despairing and despised. This is only thoughts. Yes, I must learn the lessons, and that way 1a never happens. As I deal with 1 though working on my fears, and adopting a lot more self love (fake it till ya make it), it will dispel 1a as it is inherently false in todays context. If 1 is resolved, 1a is disarmed, and 2a -> 2 no longer exist.
Bloody worth a shot aye! Imagine if you will, living day to day and enjoying it without all the hurt and worry and self deprecation etc etc. Imagine, being happy in your own skin. It is entirely possible, but it won't be easy facing your demons, but really, what choice do you have.