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Jenelle Evans isn't the only one fearful for her children's well-being in the presence of David Eason ... her ex is too, and he's relieved she finally left him.

Sources close to Nathan Griffith -- the father of Jenelle's 5-year-old son, Kaiser -- tell TMZ ... he's happy if Jenelle's happy ... and if that takes no longer being under the same roof as David, then he's all for it.

We're told Nathan was constantly worried about Kaiser's safety due to Eason's track record of violent and disturbing behavior. That's why Nathan attempted to get primary custody from Jenelle ... although, she ultimately retained it.

Our sources say Nathan thinks Jenelle is a good mom, and now that he has some peace of mind ... he's perfectly fine with her having Kaiser. We're told he also hopes co-parenting with her will be easier with David out of the picture.