Obligation in the past

[Ayon Khan]

If I realized in the past that I must have to do something, then how can I write it properly?
Example:
I thought I had to let him enter my house.
I realized I must do it.


Are my sentences grammatically correct?

 

[emsr2d2]

If I realized in the past that I [STRIKE]must have[/STRIKE] had to do something, [STRIKE]then[/STRIKE] how [STRIKE]can[/STRIKE] should I [STRIKE]write[/STRIKE] express it [STRIKE]properly[/STRIKE] grammatically?

Example:
I thought I had to let him enter my house.
I realized I must do it.

Are my sentences grammatically correct?

Both sentences are grammatically correct although I'd be more likely to use "I realised I had to do it" for the second. However, your question doesn't make something clear - are you talking about realising in the past that the thing you had to do is now also in the past at the time of speaking? The use of "I realised" can be followed by a different verb form, depending on the timing of the second half.

I realised I had to do it.
I realised I have to do it.