Past gerunds and infinitives

We use a present gerund or infinitive to show that the action of the infinitive takes place IN THE SAME TIME FRAME as the action of the verb.

We use a past gerund or infinitive to show that the action of the infinitive took place BEFORE the action of the verb.
 
1. I’m happy about being your teacher.

When am I happy? Now
When am I your teacher? Now

2. I’m happy about having been your teacher.

When am I happy? Now.
When was I your teacher? Last semester.

3. I was happy about being your teacher last semester.

When was I happy? Last semester.
When was I your teacher? Last semester.

4. I was happy last semester about having been your teacher.

When was I happy? Last semester.
When I was your teacher? Before last semester.

Present and past infinitives:

1. I'm happy to be your teacher.
When am I happy? Now.
When am I your teacher? Now.

2. I'm happy to have been your teacher.
When am I happy? Now.
When was I your teacher? Last semester.

3. I was happy to be your teacher last semester.
When was I happy? Last semester.
When was I your teacher? Last semester.

4. I was happy last semester to have been your teacher.
When was I happy? Last semester.
When was I your teacher? Before last semester.