Pregnant with baby #4.. considering abortion..

It absolutely breaks my heart that im even thinking this. I never ever thought that i could do this. But i have gastric bypass surgery soon to lose weight and repair my hiatal hernia (my entire stomach has been pushed into my chest). I have wanted nothing more for YEARS than to lose weight.. i have the opportunity now and accidentally ended up pregnant. I'm in a constant fight with myself. I have never put myself over any of my kids... but should i do this one thing for me to improve my health? I guess i just needed somewhere to rant... im so lost and heartbroken.. i feel like neither decision is the right one.