I'm a terrible mother...

I have two girls one is a year and a half the other is 2 months old...last night I gave my girls a bath we played and splashed!! the way my house is set up you can see into our bathroom from the living room kitchen and our bedroom and last night like any other night I got my youngest out to get dressed and went into the living room every few seconds I'd look up to check on my girl she was fine like always so I got up and put my youngest in her bassinet in the room to sleep then I walked out if my room checked on my oldest again then walked to the living room to get our nighttime oils and the towel when I turned around the most horrific sight I seen my babies legs up in the air as she was in the bathtub I dropped all I had ran and screamed I got in there and she was trying to sit up but you could tell she kept loosing her grip I didn't think I reached for her and snatched her out of the water into my arms I flipped her over make sure if she was coughing up any water it would come out..she didn't cough or anything she was just crying holding on to me..I grabbed another towel and wrapped her up and just held her yelling her mommy's got her and she's okay I couldn't stop crying or shaking for hours and I didn't let my baby girl outta my arms all night I just stayed up and held her..I couldn't get that split second image of my girl underwater outta my head..my boyfriend thinks I'm overreacting because she was fine after but I don't care he didn't see what i saw..I swear on everything i won't leave her for a second anymore I'm still thanking god for not taking my baby from me Idk what i would of done..I'm so sorry baby girl mommy made a mistake 💔