Yes, you get this achievement through normal progression of the game.
But if you don't have the right gear at the end you will find the final Boss battle almost impossible.
When you get to the last shop and Bench in chapter 14 you need to make sure you pick right weapons for the job ahead and buy a ton of ammo. and health. ( I can't recall if this area is before or after the first few rounds with the regenerator. I think it was after Can any one correct me on this?)
You will know this area as the bench and Shop will be opposite each other with the save point up a ramp.
You want your rig and Stasis fully upgraded here as you will need them to get through the next area to the final boss.
You'll want at least 3 stasis refills, if like me you made it through to this point with more than 6, keep 6, it will be easier.
You want at least 2 weapons fully upgraded or close to it, I had the Plasma Cutter and the Pulse rifle ( which had the primary lines fully upgraded and the aux line at the top was ignored)
I also used the Line cutter and the Javelin gun as secondary, but I hear the seeker rifle is as good as the Javelin if not better for this battle.
I took over 400 rounds for the Pulse rifle and 50 for the plasma cutter, and about 20 for the other 2, this was barely enough.
You want probably 500+ for the pulse rifle and 100 for the plasma cutter.
And you want at least 6 med health packs if you have them.
And that's just to get to the boss from this point.
You're going to fight Your way through a series of areas with Storage tanks and narrow walkways through them. You will be under attack similtaneosuly by The Regenerator, Dark Slashers, and The little tentacle guys who shoot at you. Ignore the guys shooting and just stasis and dismember everything else, then run through.
between the storage areas are small corridor intersectiosn where the regenerator will drop in front of you.
These areas also have Dark Slashers and The guys who vomit on you. Same trick here stasis and Dismember. I found the Line Guns Secondary Fire useful here .
Unless you are playing on Hardcore there are checkpoints when you enter these corridor areas.
Once you beat this area. You come to the last save point.(If your playing on Hardcore this may be the best point to use your 3rd and final save.)
Once you go through the door there are 2 areas with the fuses you need to shoot to progress. Just stasis The regen, and shoot the Fuses and run, because once you're through this area You are at a cut scene before the final battle.
Sorry you don't get to kill the Mr Regen.
For the final battle I found the the Line gun was good for taking out bunches of Stasised Shadow Babies And the Javelin gun with good use of the Secondary electrocution was good for taking out your Evil Ex.
I would fire one spear, then electrocute, then usually the second would shatter her.
Then I would switch to my Plasma Cutter or the pulse rifle (whichever I had collected ammo for) and shoot the yellow Heart glowing in the background while it was Vulnerable.
Then the Heart would close and the Evil Ex just like in real life would make an unwanted reapearance.
Watch your health during this battle as the Shadow Kids will kill you before you reach Zero health. If your Health reaches 1 bar you are dead.
If ammo is low, clear the kids, then run in circles collecting their item drops while avoiding the Ex as she just needs to be close to you to get an instant kill, no matter how much health you have.
Repeat the Heart three times at least to take it out, it may take more if you haven't fully upgraded your weapons.
Apparently a fully upgraded Seeker rifle does massive damge to the heart.
Hope this helps.