What's the meaning of surrogate

What is the meaning of surrogate means Raman will sleep with Shagun?
I felt so bad for Raman he wanted to sleep with ishita and did decorating the whole room bechara Raman he said since his brother is going for suhagrat and he also felt like romancing his wife and sleep with her as baby is on the way

I just request the cvs to not show Raman sleeping with Shagun even in dreams I don't want to see that maybe they will show Raman drunk and ends up sleeping with Shagun but I really don't want to see.