How to make "white" jello using aloe vera jelly pack for broken glass dessert
I have not seen this "aloe vera jelly" you describe, but from its behavior (clumps milk, needs a boil), it seems to be a pectin based thickener. If it is HM pectin, it will need enough acid, and this will clump the milk. 

The simple answer is that you will not be able to make a milk jelly with this thickener. Your options is to either use a different white liquid, or to use a different thickener. There aren't that many white liquids, but a nut milk might work. Especially if it's stabilized, it might not curdle under acid (but I'm not 100% sure). As for thickeners, you could try LM pectin, it will even get its calcium from the milk. Other thickeners are available, but the thickened texture will not be as gel-like, but have a somewhat different texture. Agar might work.