He is invited to go places with the kuffaar

With regard to your going with non-Muslims and doing things with them on which you do not know the rulings, we say to you the following:

It is not permissible for you to do anything that is an action belonging exclusively to the kuffaar or to join in with them in that. If you say that you do not know the ruling, we tell you that it is possible that you might join in some things with them which, according to our religion, are Kufr (disbelief), such as joining them on their festivals or fasts. Even if you are not guilty of kufr, you will not be free from committing a major sin. This is what has been stated by the imaams (major scholars) such as Ibn al-Qayyim in his book Ahkaam Ahl al-Dhimmah, and his shaykh (teacher) Ibn Taymiyah in Iqtidaa al-Siraat al-Mustaqeem.

Even if you know this, and then you do these things out of friendship towards them, you still will not be free of sin.

Shaykh Muhammad ibn Saalih al-Uthaymeen said: And whoever does any of that i.e., joining them in their festivals is a sinner, whether he does it just to be friendly, or because he is too shy to do otherwise, or for any other reason, because it is a kind of hypocrisy in the religion of Allaah and is a way of making the kuffaar feel stronger and making them proud of their religion.

(Majmoo Fataawaa wa Rasaail Fadeelat al-Shaykh Muhammad al-Uthaymeen, 3/110).

If you go with them on occasions other than their festivals to parties and gatherings in which there is dancing, singing, music, mixing and wanton display, this is haraam and is not allowed.

If you go with the kuffaar to attend normal gatherings such as scientific lectures where there is nothing haraam involved, there is nothing wrong with this, but you should be aware that mixing too much with the kuffaar may have negative consequences. Try to meet regularly with good Muslims. May Allaah help you to do all that is good.