Here's a suggestion. Experiment with other milks. Oat milk, nut milk, rice milk. It's not the same, but it's an ok substitute if you find the right flavourings that you like, eg chai tea or some such.
You don't have to drink milk before bed, have a herbal tea or kombucha or

Being lactose intolerant and drinking milk doesn't just give you stomach pain and diarrhea, it can cause lasting damage to your intestinal linings and lead to chronic illness.

Do yourself a favour and stop giving yourself the shits just because you like the taste.