I had an intercourse with my husband accidentally. But I am still feeding my baby who is 12 months old. I have underwent Tubal ligation surgery for not having babies anymore.

Can you please let me know if I can feed the baby? Will the milk get spoiled?

Yes, you can feed your baby. The breast milk does not spoil (ever) unless you've left it in the refrigerator too long. As long as you are breast feeding you will continue to produce milk unless something else is going on with your body or you get pregnant again (which in your case isn't likely). So go enjoy your husband!

There are plenty of myths about a mothers milk spoiling, none of which are true. I found a list of them online if you'd like to have a look:

Breast Feeding Myths

You do not mean you think having sex will effect the breast milk are you ? Since I don't see any sense to your question.
1. accidentally had sex? Tripped and fell on top of him ?
2. spoiled breast milk? How long is it out of the fridge or in the fridge?

You can continue to breastfeed your baby and have sex with your husband. Having sex will not effect your breastmilk in anyway. Your tubal ligation will not effect your breastmilk either.